A Quick guide to C. Dr Alun Moon September 16, Contents. Introduction 2 Unix 2 On Program design 4. C programming Good practice 4

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1 A Quick guide to C Dr Alun Moon September 16, 2014 Contents Introduction 2 Unix 2 On Program design 4 a few simple steps 4 C programming Good practice 4 File contents 4 Rob Pike rules 5 Philosopy of good programs 5 Program structure 6 External Structure 6 Internal structure 7 Processing 7 Compiling and running 8 Anatomy of a C program 8 C language 10 Variables and declaration 10 Declaration 10 Constants 10 Arithmetic expressions 11 Control flow 11 Logical values 11 Language elements 11 Arrays, Strings and pointers 13 Arrays 13 Strings 13 Arrays of strings 14 Pointers 14 Functions 15 Changing parameters using pointers 16 Using functions in separate files 16

2 a quick guide to c 2 Output and Input 17 Fields 18 Input 19 Command line 19 Standard input 20 Reading input line by line 21 File handling 21 Errors 22 Examples 23 sum 23 wordstat 24 man pages 25 Introduction C 1 is a powerful language originally developed by Dennis Ritchie for writing the Unix operating system. The examples here are shown running on a Unix system, though ports of C exist for Macs 2 and Windows. Editors A C program is just text. Any good text editor will do, emacs, vi, gedit,... 1 Brian Kerngihan and Denis Ritche. The C Programming Language. Prentice Hall, second edition, 1988; and Stephen Kochan. Programming in C. Samms, third edition, OSX is of course a Unix system (derrived from BSD) Unix C programs are written to run under Unix. any text editor, vi, emacs, gedit, scite, etc. will do. gcc is a command line tool that combines the functions of compiler assembler linker the files likely to be encountered are C source C header object executable Tools assembler converts assembly code into object files compiler converts c-code into object filrs

3 a quick guide to c 3 linker combines object files together debugger controls running of the program to allow execution of single instructions and examine contents of variables Conventions for file extensions There are a number of commonly used file extensions used in C and assembly programming. Most of these are common to all systems. The various tools assume these extensions are used..s assembler Contains assembly language instructions.c C source Contains the source code for the programme in the C programming language.h C header Contains function and variable declarations along with relevant constants.o object Contains information about the location and contents of memory

4 a quick guide to c 4 On Program design Programming is both an art and a science. It is an art in the sense of a master craftsman. In this guide I hope to introduce the thinking behind programming. It is aimed at those needing to program in C, but the skills of a programmer are independent of the language used. Remember, programming cannot be learnt by simply reading a book. It has to be learnt through practice writing programs! Take the time to practice, write your own solutions to the problems here and the exercises given. Look at my solutions, but they will be different to yours, after all I ve been doing this a lot longer. Take the time to read through and learn from my solutions. But don t forget to write your own. a few simple steps Identifying features in the program. Is the first step taking the problem into the design. It is the process of identifying what the essential functions of the program are to be. Just as important is identifying what is not needed. Breaking the problem down into smaller pieces. Most problems can be broken down into smaller pieces. Either as distinct sub-programs or as a series of tasks within a program, or even function. This functional decomposition allows a complex task to be reduced to smaller simpler pieces that fit together to perform the task. Identifying functions and writing the prototype. Once the tasks have been found, often they can be written down as the names of functions to use. With the name goes the information that the function needs and the values it returns. Writing the program logic. Once the functions are known, what they do can be transfered into the program logic. The logic for a function can be very simple or complex depending on the task. C programming Good practice File contents Program source files are simply text files. They can be worked on by any editor All an IDE does is wrap up an editor and the invocation of the tools in a single front-end. the linker control file is another text file

5 a quick guide to c 5 Corollary 1 Since source files are text, they can be created and edited by other programs. Corollary 2 (Treat programs as documents) express concepts with clarity readability comment when code is not clear reference them Rob Pike rules Rob pike wrote some rules for C 3 3 Rob Pike. Notes on programming in C URL 1. You can t tell where a program is going to spend its time. Bottlenecks occur in surprising places, so don t try to second guess and put in a speed hack until you ve proven where the bottleneck is. 2. Measure. Don t tune for speed until you ve measured, and even then don t unless one part of the code overwhelms the rest. 3. Fancy algorithms are slow when n is small, and n is usually small. Fancy algorithms have big constants. Until you know then n is frequently going to be big, don t get fancy. (Even if n does get big, use Rule 2 first.) 4. Fancy algorithms are buggier than simple ones, and they re much harder to implement. Use simple algorithms as well as simple data structures. 5. Data dominates. If you ve chosen the right data structures and organised things well, the algroithms will always be self-evident. Data structures, not algorithms, are central to programming. se/c/pikestyle.html Rob Pike was one of the team who developed Unix for which C was invented Philosopy of good programs From The Art of Unix Programming 4 1. Rule of Modularity: Write simple parts connected by clean interfaces. 2. Rule of Clarity: Clarity is better than cleverness. 4 Eric S. Raymond. The Art of Unix Programming. Professional Computing. Addison-Wesley, 1 edition, URL html/ 3. Rule of Composition: Design programs to be connected to other programs. 4. Rule Rule of Separation: Separate policy from mechanism; separate interfaces from engines. 5. Rule of Simplicity: Design for simplicity; add complexity only where you must.

6 a quick guide to c 6 6. Rule of Parsimony: Write a big program only when it is clear by demonstration that nothing else will do. 7. Rule of Transparency: Design for visibility to make inspection and debugging easier. 8. Rule of Robustness: Robustness is the child of transparency and simplicity. 9. Rule of Representation: Fold knowledge into data so program logic can be stupid and robust. 10. Rule of Least Surprise: In interface design, always do the least surprising thing. 11. Rule of Silence: When a program has nothing surprising to say, it should say nothing. 12. Rule of Repair: When you must fail, fail noisily and as soon as possible. 13. Rule of Economy: Programmer time is expensive; conserve it in preference to machine time. 14. Rule of Generation: Avoid hand-hacking; write programs to write programs when you can. 15. Rule of Optimization: Prototype before polishing. Get it working before you optimize it. 16. Rule of Diversity: Distrust all claims for one true way. 17. Rule of Extensibility: Design for the future, because it will be here sooner than you think. Program structure There are a number of repeated patterns that occur in programs. These are both how the program interacts with the outside world and the internal structure of the program. Understanding how these patterns work and applying them to the implemetation of probles is the key to effective programming. External Structure Input and output The first layer of patterns is how the program interacts with the outside world. Most programs can be thought of as a filter, transforming input into output. input Program output

7 a quick guide to c 7 Cooperating programs Programs can be designed to act together, the output from one becomes the input to the next. The actual mechanism is handled by the outside environment. input Program a Program b output Corollary 3 The upshot of this is that the formats of the input and output data are important in designing a program. Corollary 4 Design programs to cooperate. Corollary 5 Sometimes a problem can be split into separate cooperating programs. Internal structure There are two basic patterns that are useful at this stage for thinking about the internal structure of a program. These can apply at any level Most programs have the same basic internal structure. 1. initialise the program. Set up data structures, parameters and constants. 2. process perform the operations of the program. 3. finish clean up after the program. initialise process finish This pattern applies at any scale, the program as a whole, a function, a loop within a block of code. Processing The processing performed by the program follows a similar pattern 1. read some data 2. process the data 3. write the results. Usually there is some loop wrapped around this pattern. Depending on the problem the processing can occur for each item read, or all the data needs to be read before the processing can occur.

8 a quick guide to c 8 read process write Compiling and running Consider the following program saved in the file hello.c hello.c main() printf("hello, world\n"); The C compiler is gcc, it produces an executable file that can be used as a Unix command. By default the file is called a.out, as shown below alun@debian:~$ gcc hello.c alun@debian:~$ a.out Hello, world alun@debian:~$ The -o switch can be used to set the name of the output file alun@debian:~$ gcc -o hello hello.c alun@debian:~$ hello Hello, world alun@debian:~$ Anatomy of a C program Looking at the hello, world program above and the example below, several features of C can be seen.

9 a quick guide to c 9 /* A program to print out the arguments to main. It illustrates how the command line input is split into words, and assigned to the argc and argv parameters to main. */ int main (int argc, char *argv[]) int i; for (i = 0; i <= argc; ++i) printf ("argument %i=%s\n", i, argv[i]); #include both programs start with a #include statement. This is similar to the role of the import statement in Java. It makes declarations of functions available to the program. The file ending in.h is often called a header file. There are two forms for quoting the filename, which determines where the file is looked for. 1. Angle brackets <name> looks first in system directories for standard header files 2. Double quotes "name" looks in the current directory first. main both programs have a main function which is the program entry point. Java has the static public void main method. Unlike java there are three forms. 1. main() is the simplest. No command-line arguments are passed to the function. Although no return type is given an int is assumed. I wouldn t recomment this form as not giving a return type is not good practice. 2. int main() is the same as the first, but with an explicit return type. 3. int main(int argc, char *argv[]) is the third form. The command-line is split into words (using spaces) and the words placed in argv, while argc has the number of words. For more details see. statements end with a semicolon. declarations of variables are the same as in Java. The type name, followed by the variable name, then an optional initial value. block structure C has a block structure for function bodies, loop and conditional (if statement) bodies. A block is a series of statements enclosed within braces and. In the case of a loop or

10 a quick guide to c 10 if statement if the block has a single statement, then the enclosing braces can be omitted. There is some debate as to whether it is good style to use braces or not for a single statement block, it may be better to always use braces for consistency, as in. for(i=0 ; i<=argc ; ++i) printf("argument %i=%s\n", i, argv[i]); comments begin with a /* and end with a */ C language In some respects you will find C similar to Java. Which is not surprising as the syntax of Java was inspired by C. Variables and declaration The basic data types in C are char single byte, capable of holding one character int an integer, typically reflecting the natural size of integers on the host machine In addition integer variables (char and int) can be declared as signed or unsigned. Signed variables use the same number of bits as unsigned variables, but the signed ones use two s-complement arithmetic. The big difference between types in C and Java is the number of bits used. In Java an int is always 32bits, whereas in C an int is whatever a word of memory is (at least 16 bits). There are also floating point numbers for non-integer arithmetic. Declaration Declaring variables occurs the same way as in Java, the type is followed by a variable name. Names are case-sensitive in C. int width, length, height; float initialprice = 45.2f; char tab = \t ; Constants Constant values for each of the basic data types can be written according to the following table. char a \n \x3f etc int 1234 float 123.4f 4.34e4f note the f suffix double e4

11 a quick guide to c 11 Arithmetic expressions Arithmetic expressions in C are much the same as in Java. The only difference is that in Java exceptions can be throws for errors such as divide-by-zero, in C the program will crash and die. All the arithmetic and logical operators from Java are available in C. The type of the result depends on the types of the operands, the result has the broadest type of the operands where int is promoted to float and float to double as needed. The modulus operator % only acts on integer types. Be careful when using division; with integer types integer division is performed (5/2 = 2), whereas with one or more floats floating point division is performed (5.0/2 = 2.5). Control flow C has the usual control flow supported by Java, if, switch, for and while. Logical values C has no boolean type as Java does. The following convention is used to interpret integer values zero false not zero true The usual comparison and logical operators are provided (<=, ==, && etc). Language elements if The if statement has the form if ( expression ) statement block If the expression is non-zero the statement block is executed. if... else The if... else statement has the form if (expression) statement block 1 else statement block 2 If the expression is non-zero the first statement block is executed, if zero the second is executed. if... else if... If statements can be used as the second block creating a multi-way choice. if ( expression 1 ) statement block 1 else if ( expression 2 ) statement block 2

12 a quick guide to c 12 else if ( expression 3 ) statement block 3 else if ( expression 4 ) statement block 4 else statement block 5 switch As in Java the switch statement allows a multi-way test. The value tested must be an integer or char, as must be the values in each case. The break keyword is needed to exit the switch, without it all the subsequent statements in the switch will be executed until the switch exits. switch (c) case n : statements break; case t : statements break; case f : statements break; default: statements for The for loop is the same as in Java, except that the loop variable must be declared outside the for loop. for( initial value ; continuation condition ; increment ) statement block while The while loop is identical and behaves the same way as the while loop in Java. This is often used is reading a file. /* read and process input line-by-line */ const int LINEBUFFER = 80; /* define a length of a line buffer */ char line[linebufer]; /* declare a buffer to read lines into */ main() while( fgets(stdin, LINEBUFFER, line) ) /* process line */

13 a quick guide to c 13 Arrays, Strings and pointers Arrays, strings and pointers are all related in C. Arrays are declared and used as in Java. Once created array sizes cannot be changed. Unlike Java there are no checks used on the array index to see if it is within an array. Once an array has been created, there is no way to find its length using a.length attribute as in Java. Arrays The following example fills an array with squares of numbers and then prints them out in reverse order. main() const int LISTSIZE = 10; int squares[listsize]; int i; for( i=0 ; i<listsize ; ++i) squares[i] = i*i; for( i=listsize-1 ; i>=0 ; --i ) printf("%2d squared is %3d\n",i,squares[i]); Arrays can be initialised in the declaration, in these cases the size is given implicitly in the data. char int daysinmonth[] = 31,28,31,30,31,30,31,31,30,31,30,31; This allocates space for 12 integers, and fills the array with the given values. Strings C has no string data type or class. Strings are represented as arrays of char. Strings are stored as a series of ASCII codes in the char array, the end of the string is marked by a zero byte \0. So for a given length of string, an array needs one more space to store the zero byte. The following declarations establish strings. char buffer[1024]; char message[] = "hello, world\n"; char *greeting = "salutations"; The first form allocates 1024 bytes of uninitialised space. The second allocates 14 bytes, the 13 in the string literal and the ter-

14 a quick guide to c 14 minating zero byte. The last form allocates 12 bytes, the 11 in the word and the zero terminating byte. Strings cannot be manipulated as in Java or C++. The <strings.h> library provides several functions that are of use. strlen calculate the length of a string strcat concatenate two strings strcpy copy a string Beware: when using the strcpy and strcat functions, the destination array must have enough space allocated. There is no protection against overflowing the space into random memory. Not checking data to avoid these kinds of overflows is the main cause of vulnerabilities to attacks by viruses, worms and similar hostile programs. There are versions of copy and concatenate that have length checks, strncpy and strncat. These specify the maximum number of characters to copy. Arrays of strings Arrays of strings are simply arrays of pointers to char. The following three declarations are equivalent. char days[][]; char *months[]; char **years; The difference is how the sizes are allocated. All forms can be subsequently be used in similar ways. An array of strings can be initialised as follows. char **daysofweek = "Monday", "Tuesday", "Wednesday", "Thursday", "Friday", "Saturday", "Sunday" ; One common use of an array of strings is the arguments passed to main. Pointers Pointers are variables that refer to the location data is stored at. Given a variable a, the ampersand operator get the location of a, the star operator gets the value the pointer points to.

15 a quick guide to c 15 main() int a = 5; int b = 2; int c; int *p; /* a pointer to an int */ printf("a = %i, b = %i, c = %i\n",a,b,c); p = &a; /* p points to a */ c = *p; /* c now equals a */ *p = b; /* a now equals b */ printf("a = %i, b = %i, c = %i\n",a,b,c); Pointers have their main uses in functions and input (see below). NULL pointers. many system functions return pointers. Usually if the function cannot complete its operation, then a pointer with the NULL value is returned (defined in several header files). Functions Functions in C are equivalent to methods in Java. Because C is not object oriented, there is no public or private qualifier. A function is declared with a return type, a name, and a parameter list. int square(int x) return x*x; Defines a function called square that takes a single integer argument, and returns the square (x 2 ) of the value. The parameters passed to a function can be changed in the function, but this is not reflected in the variable outside the functions. int cube(int x) x = x*x*x; return x; Returns the cube of a number. If it is called as follows, int n=3; cube(n);

16 a quick guide to c 16 returns the cube of n, but the value of n is unchanged in the calling program. Function parameters are said to be passed by value. The parameter given in the function call is evaluated and the resulting value copied into the variable declared in the function definition. Changing parameters using pointers If the value of a parameter needs to be changed, this can be done by using a pointer as a parameter. For example if the value of an integer needs to be halved this can be done as follows. void halve(int *n) *n /= 2; remember: a /= 2 is equivalent to a = a/2 To call the function you can only use a variable 5 and must pass the address of the variable. As follows: 5 Not an expession int n = 4; halve(&n); Using functions in separate files The program can be split into several files. Often related functions are collected into a single library. In order to use a function, it needs to be declared before it can be used. int max(int a, int b); /* declaration of max */ main() int p = 5; int q = 8; printf("%i\n", max(p,q) ); int max(int a, int b) /* definition of max */ return (a>=b)?a:b; The max function can be put into a separate file, which we will call libmax.c. The convention is to have a header file sharing the base-name containing the declarations.

17 a quick guide to c 17 libmax.c int max(int a, int b) /* definition of max */ return (a>=b)?a:b; libmax.h int max(int a, int b); /* declaration of max */ The function is then used by including the header file in the program where it is used and compiling the two files. #include "libmax.h" main() int p = 5; int q = 8; printf("%i\n", max(p,q) ); The two can be compiled together simply by passing both filenames to the compiler. alun@debian:~$ gcc -o usemax usemax.c libmax.c alun@debian:~$ usemax 8 alun@debian:~$ The library can be compiled separately. The compiler -c option is used, it creates an object file with the same base-name and a.o extension. The object file can then be used in a separate use of the compiler with the main program. alun@debian:~$ gcc -c libmax.c alun@debian:~$ gcc libmax.o usemax.c -o usemax alun@debian:~$ usemax 8 alun@debian:~$ Output and Input The IO library in C is stdio, to use it include the system header file. The basic output function is printf. It prints the string supplied

18 a quick guide to c 18 to the function on stdout, note that the newline has to be given explicitly in the string using the \n sequence. Fields printf can format and print numbers and text. The place for the value is introduced by a % sign, the type of the variable to be printed is given by a letter as follows i integer f floating point s string (char array) The general format of the placeholder is % width. precision type where the width is the minimum number of characters to use, precision is the number of decimal places to use, and type is a letter as above. For example the program, int main() int n=5; printf(" %d \n",n); printf(" %5d \n",n); printf(" %05d \n",n); printf(" %-5d \n",n); float p= 1.0/6.0; printf(" %f \n",p); printf(" %6f \n",p); printf(" %6.2f \n",p); printf(" %-6.2f \n",p); produces For strings the precision is the maximum number of characters to use from the string.

19 a quick guide to c 19 main() char *sample = "This is a bit of sample text!"; printf(" %s \n",sample); printf(" %10s \n",sample); printf(" %40s \n",sample); printf(" %-40s \n",sample); printf(" %20.10s \n",sample); printf(" %.10s \n",sample); produces This is a bit of sample text! This is a bit of sample text! This is a bit of sample text! This is a bit of sample text! This is a This is a Input There are two ways of getting input into your program, commandline arguments, and the stdio library. The command line arguments are quick and easy, useful for giving initial data to the program. The stdio functions are more flexible. Command line The command line is passed into the program via arguments to main, an example program and its output are shown below. /* A program to print out the arguments to main. It illustrates how the command line input is split into words, and assigned to the argc and argv parameters to main. */ int main (int argc, char *argv[]) int i; for (i = 0; i <= argc; ++i) printf ("argument %i=%s\n", i, argv[i]);

20 a quick guide to c 20 alun@debian:~$ cmd this is a sample line argument 0=cmd argument 1=this argument 2=is argument 3=a argument 4=sample argument 5=line argument 6=(null) alun@debian:~$ The first parameter to main receives the number of words in the command-line. The input is split into words using spaces as separators. The second parameter is an array of strings (pointers to characters). The first element is the name of the program, the array has a null pointer after the last command-line argument. Standard input The basic input function in stdio is scanf. It uses the same strings to indicate data to be read. The width and precision are interpreted differently. The major difference between input and output is that pointers to variables are needed in order to store the values read. For variables such as integers remember to use the ampersand, scanf("%i",&a) where a is an integer int a. For strings the array name is also a pointer, so the ampersand is not needed scanf("%s",name), where name is a string char name[8]. Remember to allocate space for a string to be read into! Type letters The same letters are used to indicate the type of data being read as printf d integer i integer f floating point s string (non-whitespace) The string type will read as many non-whitespace characters as possible. The d type reads an integer. The i type also reads an integer, but will cope with hexadecimal numbers that start with 0x (0xABCD) and octal values that start with a 0 (0777). The rest of the format string works as follows. Any whitespace characters match any amount of whitespace in the input. Nonwhitespace characters are expected to match the next exact character in the input. For example scanf("from: %s",addr) will match and read the senders address in a message, but not match the subject line. Because of the way whitespace is read, output formated with the string "%5d %5d" can be read with the string " %d %d".

21 a quick guide to c 21 Reading input line by line The scanf family of functions do not recognise the end of a line, successive calls to scanf keep reading input reading across lines if needed. A safe way to read a file line by line is to use the fgets function. It is recommended to use fgets as the maximum number of characters to be read can be given, avoiding buffer overflows. The following is a template to read a file, one line at a time. enum BUFFERSIZE = 132; /* makes a constant integer */ char buffer[buffersize]; /* buffer to read lines into */ main() while( fgets(buffer, BUFFERSIZE, stdin) ) /* process line here... */ The line can then be processed using sscanf a variant of scanf that reads from a string rather than input. sscanf(buffer, "%s %s", name, class); reads two strings (name and class) from the string buffer (from above), separated by whitespace. Of course this will not cope where the name has any spaces. fred jones M8 will be read as the name being fred the class being jones. Getting round this limitation of scanf is part of the art of designing C programs and the data structures used for files File handling So far all the functions have operated on standard input and standard output. One trivial way of reading or writing to files is to use shell redirection alun@debian:~$ classes < data > results alun@debian:~$ runs the program classes reading from the file data instead of standard input and writing to the file results instead of standard output. The standard IO library provides a number of types and functions to support reading and writing files. File handles: are used to manage files. Pointers to these are returned by the fopen function and passed to the other functions. fopen returns a file handle pointer. It takes two parameters, a filename string and a mode string. Some of the mode strings 6 are 6 try man 3 fopen for more details

22 a quick guide to c 22 r open for reading w open for writing, setting the length to zero and deleting any existing contents overwrites a file w+ As for w but creates the file if if does not exist. a Open for appending, output is added to the end of the file. fopen returns either a valid file-handle or NULL if some error has occurred. The return value should always be tested. fclose is used to close a file once it has been finished with. Programs should always clean up after themselves by closing open file-handles. fprintf writes data to the file. A pointer to file-handle supplied by fopen is passed as the first parameter, the second is a printf format string, the remaining parameters are the data for the format string as in printf. fscanf reads from an open file. The first parameter is a pointer to a file handle, the rest are as for scanf. Errors Occasionally errors may occur, such as an attempt to open a non existent file for reading. Depending on the function different values are returned to indicate an error. Read the man page for the function to find out what return value indicates an error, and test for it. Often the variable errno (from errno.h) is set to indicate the kind of error. Test the return value for the function 7 not errno. A function perror prints a specified message to standard-error along with the corresponding error-message for errno. Rather than using return, there is an exit function (in stdlib.h) that causes the program to exit and causes some default cleanup. It also defines two constants EXIT_SUCCESS and EXIT_FAILURE to indicate the success of the program. 7 if in doubt check the man pages

23 a quick guide to c 23 Examples sum The following example reads a column of numbers from a file and prints the sum at the bottom of the file. #include <stdlib.h> #include <errno.h> #include <strings.h> int main( int argc, char **argv ) enum BUFSIZE=132; char line[bufsize]; FILE *data; int d, total=0; if (argc<2) exit(exit_failure); /* no filename given, return a failure exit code*/ data = fopen(argv[1],"r"); if( data == NULL ) perror("sum cannot open a file"); exit(exit_failure); while( fgets(line, BUFSIZE, data) ) sscanf(line,"%i",&d); total+=d; fclose(data); /* a more compact file open */ if(!(data=fopen(argv[1],"a")) ) perror("can t open file for appending"); exit(exit_failure); fprintf(data," \n%8d\n",total); fclose(data);

24 a quick guide to c 24 wordstat The following example reads a series of words 8. It counts the words read and maintains a record of the longest word read. 8 remember a word is a nonwhitespace sequence of characters #include <stdlib.h> #include <strings.h> #include <errno.h> int main( int argc, char **argv) enum WORDBUFERSIZE=80; char word[wordbufersize]; FILE *data; int words=0, maxlen=0; if(argc<2) exit(exit_failure); if (!(data = fopen(argv[1],"r")) ) perror("wordstat can t open a file"); exit(exit_failure); while( fscanf(data,"%s",word)!=eof ) if (strlen(word)>maxlen) maxlen=strlen(word); ++words; printf("%d words, max length %d characters\n",words, maxlen); fclose(data);

25 a quick guide to c 25 man pages All the C functions are documented in section 3 of the Unix Programmers Manual. To read the page for printf use; alun@debian:~$ man 3 printf alun@debian:~$ References Brian Kerngihan and Denis Ritche. The C Programming Language. Prentice Hall, second edition, Stephen Kochan. Programming in C. Samms, third edition, Rob Pike. Notes on programming in C URL lysator.liu.se/c/pikestyle.html. Eric S. Raymond. The Art of Unix Programming. Professional Computing. Addison-Wesley, 1 edition, URL org/esr/writings/taoup/html/.