1. We have a code sequence that is potentially executed twice.

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1 Long Jump Long Jump Local Jumps In the following example: 1. We have a code sequence that is potentially executed twice. 2. A flag is used to determine whether the sequence is being executed the first or second time. 3. A series of loops establishes the context of the main body of code. 4. If an error occurs a goto is executed which jumps out of the nested loop context and back to a prior point in the sequence. int main( void ) int array[dim1][dim2][dim3]; int second_time = 0; int inx = 0; int jnx = 0; int knx = 0; start: if ( second_time ) puts( "error!" ); exit( EXIT_FAILURE ); (continued) Long Jump file:///c /Documents%20and%20Settings/Jack%20Straub/M...20Work/AdvancedC/Binders/150LongJump/110LongJump.html [3/29/ :12:18 AM]

2 Long Jump Long Jump Local Jumps (continued) for ( inx = 0 ; inx < DIM1 ; ++inx ) for ( jnx = 0 ; jnx < DIM2 ; ++jnx ) for ( knx = 0 ; knx < DIM3 ; ++knx ) char buff[80]; char *err = NULL; int num = 0; printf( "> " ); fflush( stdout ); fgets( buff, 80, stdin ); num = (int)strtol( buff, &err, 0 ); if ( *err == '\n' *err == '\r' ) array[inx][jnx][knx] = num; else second_time = 1; goto start; process( array ); return EXIT_SUCCESS; Long Jump file:///c /Documents%20and%20Settings/Jack%20Straub/M...20Work/AdvancedC/Binders/150LongJump/120LongJump.html [3/29/ :12:18 AM]

3 Long Jump Long Jump Nonlocal Jumps In this example we do the same thing except that we want to jump back to a point in a prior stack frame: 1. We use setjmp to save the context of the stack frame in a global buffer; 2. The value returned by setjmp() tells us which time we are passing through the code; 0 means the first time; 3. If an error occurs longjmp() is executed which restores the saved context; 4. When the context is restored it appears as though we are returning from setjmp() once again; a non-zero return value tells us that it is not the first time. static jmp_buf jump_context_; int main( void ) int array[dim1][dim2][dim3]; if ( setjmp( jump_context_ )!= 0 ) puts( "error!" ); exit( EXIT_FAILURE ); (continued) Long Jump file:///c /Documents%20and%20Settings/Jack%20Straub/M...20Work/AdvancedC/Binders/150LongJump/130LongJump.html [3/29/ :12:18 AM]

4 Long Jump Long Jump Nonlocal Jumps (continued) static void filldim1( int arr[dim1][dim2][dim3] ) int inx = 0; for ( inx = 0 ; inx < DIM1 ; ++inx ) filldim2( arr, inx ); static void filldim2( int arr[dim1][dim2][dim3], int dim1 ) int inx = 0; for ( inx = 0 ; inx < DIM2 ; ++inx ) filldim3( arr, dim1, inx ); static void filldim3( int arr[dim1][dim2][dim3], int dim1, int dim2 ) int inx = 0; for ( inx = 0 ; inx < DIM3 ; ++inx ) char buff[80]; char *err = NULL; int num = 0; printf( "> " ); fflush( stdout ); fgets( buff, 80, stdin ); num = (int)strtol( buff, &err, 0 ); if ( *err == '\n' *err == '\r' ) arr[dim1][dim2][inx] = num; else longjmp( jump_context_, 1 ); Long Jump file:///c /Documents%20and%20Settings/Jack%20Straub/M...20Work/AdvancedC/Binders/150LongJump/140LongJump.html [3/29/ :12:18 AM]

5 Long Jump Long Jump Long Jump Sometimes referred to as non-local goto. Must be primed via setjmp() which saves the application context. Executed via longjmp(), which makes it appear as if setjmp is returning again. The first return from setjmp() is always 0; subsequent returns are always non-0. Previous two examples may be found in the Sample Code pages. Long Jump file:///c /Documents%20and%20Settings/Jack%20Straub/M...20Work/AdvancedC/Binders/150LongJump/150LongJump.html [3/29/ :12:19 AM]

6 Long Jump Long Jump int setjmp( jmp_buf env ); Saves the application context in preparation for a longjmp. env Buffer in which the context is to be saved. Returns: 0 on the initial return to setjmp, non-zero for subsequent returns. void longjmp( jmp_buf env, int status ); Restores the application context previously saved by setjmp(). env Buffer containing saved context. status value to be returned by setjmp; if 0 is specified, the system will force it to a non-zero value. Long Jump file:///c /Documents%20and%20Settings/Jack%20Straub/M...20Work/AdvancedC/Binders/150LongJump/160LongJump.html [3/29/ :12:19 AM]

7 Answers to the Sample Final C Programming: Advanced Answers to the Sample Final 1. typedef struct grade_s char name[71]; double grade; GRADE_t, GRADE_p_t; 2. typedef int FUNK_t( const char*, const char* ); 3. char str[512] = "all: dogs, bark"; int inx = 0; char *token[5]; token[inx] = strtok( str, ":," ); while ( token[inx++]!= NULL && inx < 5 ) token[inx] = strtok( NULL, ":," ); 4. #define MAX_STR_LEN (5) static void next_step( const char *martha ) char george[max_str_len + 1]; strncpy( george, martha, sizeof(george) ); george[max_str_len] = '\000'; static int to_int( const char *str ) char *temp = NULL; long lnum = 0; int num = 0; errno = 0; lnum = strtol( str, &temp, 0 ); if ( errno == 0 && (lnum > INT_MAX) (lnum < INT_MIN) ) errno = ERANGE; if ( errno!= 0 ) file:///c /Documents%20and%20Settings/Jack%20Straub/...ork/AdvancedC/Binders/200SampleFinal/100Answers.html (1 of 5) [3/29/ :12:19 AM]

8 Answers to the Sample Final printf( "int conversion error %d: %s\n", errno, strerror( errno ) ); else if ( *temp!= '\000' ) printf( "int conversion error: string contains nonnumeric value\n" ); else if ( *str == '\000' ) printf( "int conversion error: empty string\n" ); else num = (int)lnum; return num; 6. #ifdef MAX #undef MAX #endif #define MAX (32) 7. assert( result >= 7 && result <=15 ); return result; 8. See: 9. See: C source code: samples.c Formatted html: samples.c C source code: coords.c Formatted html: coords.c 10. int main( void ) int rcode = EXIT_SUCCESS; void *temp = NULL; void *mem = malloc( 512 ); if ( mem == NULL ) abort(); temp = realloc( mem, 2048 ); if ( temp == NULL ) abort(); printf( "%s\n", (mem == temp? "extended in place" : "new block allocated") file:///c /Documents%20and%20Settings/Jack%20Straub/...ork/AdvancedC/Binders/200SampleFinal/100Answers.html (2 of 5) [3/29/ :12:19 AM]

9 Answers to the Sample Final ); free( temp ); return rcode; 11. See: C source code: funk_array.c Formatted html: funk_array.c 12. See: Answer 13. typedef int FUNKB_PROC_t( char* ); typedef FUNKB_PROC_t *FUNKB_PROC_p_t; typedef FUNKB_PROC_p_t FUNKA_PROC_t( char*, FUNKB_PROC_p_t ); 14. static unsigned adder( unsigned num ) if ( num > 0 ) num = num + adder( num - 1 ); return num; 15. See: C source code: int_search.c Formatted html: int_search.c 16. Solution is left as an exercise for the student. 17. Solution is left as an exercise for the student. 18. Solution is left as an exercise for the student. 19. #define LARGEST( a, b, c ) \ ((a) > (b)? ((a) > (c)? (a) : (c)) : ((b) > (c)? (b) : (c))) 20. #ifndef NDEBUG #define MY_ASSERT( e ) \ ((e)? (void)0 : my_assert( #e, FILE, LINE, DATE, TIME )) #else #define MY_ASSERT( e ) ((void)0) file:///c /Documents%20and%20Settings/Jack%20Straub/...ork/AdvancedC/Binders/200SampleFinal/100Answers.html (3 of 5) [3/29/ :12:19 AM]

10 Answers to the Sample Final #endif static void my_assert( const char *expr, const char *file, int line, const char *date, const char *time ) fprintf( stderr, "ASSERTION FAILURE; %s: %s:%d, %s %s\n", expr, file, line, date, time ); abort(); 21. Example 1, building a linked list from scratch: C source code: singlylinked.c Formatted html: singlylinked.c Example 2, building a linked list using the SLIST module: C source code: singlylinked2.c Formatted html: singlylinked2.c 22. a) 25 b) unpredictable c) Unpredictable 24. See: C source code: test_longjmp.c Formatted html: test_longjmp.c 25. int main( void ) int rcode = EXIT_SUCCESS; if ( atexit( atexit_proc )!= 0 ) printf( "eh?\n" ); return rcode; static void atexit_proc( void ) file:///c /Documents%20and%20Settings/Jack%20Straub/...ork/AdvancedC/Binders/200SampleFinal/100Answers.html (4 of 5) [3/29/ :12:19 AM]

11 Answers to the Sample Final puts( "atexit proc called" ); Sample Final Answers file:///c /Documents%20and%20Settings/Jack%20Straub/...ork/AdvancedC/Binders/200SampleFinal/100Answers.html (5 of 5) [3/29/ :12:19 AM]

12 Answers to the Sample Final C Programming: Advanced Answer mod.h #ifndef MOD_H #define MOD_H extern int mint; void modb( void ); void modc( void ); #endif moda.c #include <stdlib.h> #include <stdio.h> #include <mod.h> int mint = 42; int main( void ) int rcode = EXIT_SUCCESS; modb(); modc(); printf( "mint = %d\n", mint ); return rcode; modb.c file:///c /Documents%20and%20Settings/Jack%20Straub/...ork/AdvancedC/Binders/200SampleFinal/150Externs.html (1 of 2) [3/29/ :12:20 AM]

13 Answers to the Sample Final #include <stdio.h> #include <mod.h> void modb( void ) int new_val = 25; printf( "mint = %d; changing to %d\n", mint, new_val ); mint = new_val; modc.c #include <stdio.h> #include <mod.h> void modc( void ) int new_val = -9; printf( "mint = %d; changing to %d\n", mint, new_val ); mint = new_val; Sample Final Answers file:///c /Documents%20and%20Settings/Jack%20Straub/...ork/AdvancedC/Binders/200SampleFinal/150Externs.html (2 of 2) [3/29/ :12:20 AM]

14 type funk_name( type,... ); A variable length argument list must have at least one argument of a fixed type; it may have 0 or more additional arguments of any type; all fixed arguments must precede variable arguments. file:///c /Documents%20and%20Settings/Jack%20Straub/My...ol%20Work/AdvancedC/Binders/250VarArgs/110StdArgs.html [3/29/ :12:20 AM]

15 Writing a Function with a Variable Length Argument List 1. Include stdarg.h. 2. You must have some way to know the type of each argument in the argument list. In the example below it is expected that every argument is type const char*. 3. You must have some way to know when you have processed the last argument in the argument list; in the example below, it is assumed that the last argument is a NULL pointer. vfunk( "str1", "str2", "str3", NULL ); 4. Declare a pointer to the argument list with the macro va_list. va_list arglist; 5. Initialize the pointer to the argument list using the macro va_start; the first va_start argument is the pointer to the arglist, the second is the name of the last fixed argument in the list. va_start( arglist, first ); 6. Access additional, sequential arguments with the va_arg macro; the first va_arg argument is the pointer to the arglist; the second is the type of the next argument in the list. arg = va_arg( arglist, const char * ); 7. When you're finished use the va_end macro to clean up loose ends; the one argument to the macro is the pointer to the argument list. va_end( arglist ); (continued...) file:///c /Documents%20and%20Settings/Jack%20Straub/My...ol%20Work/AdvancedC/Binders/250VarArgs/120StdArgs.html [3/29/ :12:20 AM]

16 Writing a Function with a Variable Length Argument List (continued) #include <stdlib.h> #include <stdio.h> #include <stdarg.h> static void vfunk( const char *,... ); int main( void ) int rcode = EXIT_SUCCESS; vfunk( "str1", "str2", "str3", NULL ); return rcode; static void vfunk( const char *first,... ) va_list arglist; const char *arg = first; va_start( arglist, first ); while ( arg!= NULL ) puts( arg ); arg = va_arg( arglist, const char * ); va_end( arglist ); $./a str1 str2 str3 file:///c /Documents%20and%20Settings/Jack%20Straub/My...ol%20Work/AdvancedC/Binders/250VarArgs/130StdArgs.html [3/29/ :12:20 AM]

17 Another Example int george = 5; double harry = 13.7; fprintf( stdout, "george = %d, harry = %lf", george, harry );... int fprintf( FILE *file, const char *format,... ) In this example fprintf declares a pointer to an argument list and then initializes it. It has two fixed arguments, so it uses the second one in the initialization: va_list args; va_start( args, format ); 2. Next it searches through the format string looking for %. The first one it finds is followed by d so it fetches the next argument on the assumption that it is type int: if ( strcmp( token, "d" ) == 0 int_arg = va_arg( args, int ); 3. The next % is followed by lf so it assumes that the next argument is type double: if ( strcmp( token, "lf" ) == 0 dbl_arg = va_arg( args, double ); 4. Finding no more % signs it assumes there are no more arguments and performs cleanup: va_end( args ); file:///c /Documents%20and%20Settings/Jack%20Straub/My...ol%20Work/AdvancedC/Binders/250VarArgs/140StdArgs.html [3/29/ :12:21 AM]

18 Use variable length argument lists conservatively; they essentially eliminate type checking by the compiler. typedef enum actions_e action0, action1, action2, action3, action4 ACTIONS_e_t; /* This function accepts a list of actions to perform. * Each action consumes 0 or more additional arguments. * The last argument of each action is followed by * another action value until action0 is encountered, * at which point processing terminates. For example: * exec_actions( action1, 10, "geronimo", * action3, 3.14, * action4, 22, 2.2, 32, "department l", * action0 * ); * A description of each action and its respective * arguments follows. * action description * * action1 There will be two additional arguments * of type int and char* respectively... * * action2 There will be no additional arguments... * * action3 There will be one additional argument * of type double... * * action4 There will be additional arguments of * type int, double, int and const char * * * action5 This action takes any number of * additional arguments of type int, the * last one of which must be *... */ void exec_actions( ACTIONS_e_t action,... ); file:///c /Documents%20and%20Settings/Jack%20Straub/My...ol%20Work/AdvancedC/Binders/250VarArgs/150StdArgs.html [3/29/ :12:21 AM]

19 vprintf Family int vprintf( const char *format, val_list args ); int vfprintf( FILE *file, const char *format, va_list args ); int vsprintf( char *str, const char *format, va_list args ); These function work like their printf family counterparts except that they accept a va_list in place of the usual arguments that follow the format string. int main( void ) int rcode = EXIT_SUCCESS; write_args( "sally.txt", "%s was %d years old and %s was %d,\n", "Sally", 10, "Timmy", 8 ); write_args( "sally.txt", "but %s was %lf centimeters taller than %s.\n", "Timmy", 3.2, "Sally" ); write_args( "sally.txt", "\"Oh no!,\" said %s, \"something must be done.\"\n", "Sally" ); write_args( "sally.txt", "%s gazed at %s with a look of pure evil.\n", "Sally", "Timmy" ); return rcode; static void write_args( const char *path, const char *format,... ) va_list arglist; FILE *file = NULL; va_start( arglist, format ); if ( (file = fopen( path, "a" )) == NULL ) file:///c /Documents%20and%20Settings/Jack%20Straub...20Work/AdvancedC/Binders/250VarArgs/160VPrintf.html (1 of 2) [3/29/ :12:22 AM]

20 abort(); vfprintf( file, format, arglist ); fclose( file ); va_end( arglist ); $./a $ cat sally.txt Sally was 10 years old and Timmy was 8, but Timmy was centimeters taller than Sally. "Oh no!," said Sally, "something must be done." Sally gazed at Timmy with a look of pure evil. file:///c /Documents%20and%20Settings/Jack%20Straub...20Work/AdvancedC/Binders/250VarArgs/160VPrintf.html (2 of 2) [3/29/ :12:22 AM]

21 Notes 1. Don't confuse stdargs with varargs. The ISO standard is stdargs. 2. Use variable length argument lists conservatively. 3. The va_arg macro can be picky; the type argument must be composed so that adding an asterisk (*) to the end will be interpreted as "pointer to...." 4. Always use the va_end macro. In some environments this macro is not needed, but to keep your code portable it must be there. file:///c /Documents%20and%20Settings/Jack%20Straub/My...hool%20Work/AdvancedC/Binders/250VarArgs/170Notes.html [3/29/ :12:22 AM]

22 Topics About the C Miscellaneous Directives Macro Expansion file:///c /Documents%20and%20Settings/Jack%20Straub/My%2...k/AdvancedC/Binders/260/110.html [3/29/ :12:22 AM]

23 About the C Traditionally a process that runs separately from the compiler. Output from the preprocessor usually feeds directly into the compiler. Sometimes it is helpful to examine the output of the preprocessor (consult your compiler documentation for how to do this): adhoc.c /* This is a bad macro used for illustration */ #define SQUARE( x ) (x * x) int funk( void ) int inx = 5; int jnx = SQUARE( inx + 1 ); int funk( void ) int inx = 5; int jnx = (inx + 1 * inx + 1); file:///c /Documents%20and%20Settings/Jack%20Straub/My...20Work/AdvancedC/Binders/260/120About.html [3/29/ :12:22 AM]

24 About the C It may be convenient to use the preprocessor as a utility apart from compiling code. adhoc.c #define SITE " #define LINKTO( name, addr ) \ <a href = addr> \ name \ </a> <html> <head> </head> <body> <p> For more information see LINKTO( this, SITE ). </body> </html> $ gcc -E -P adhoc.c <html> <head> </head> <body> <p> For more information see <a href = " this </a>. </body> </html> file:///c /Documents%20and%20Settings/Jack%20Straub/My...20Work/AdvancedC/Binders/260/130About.html [3/29/ :12:23 AM]

25 Miscellaneous Directives #line Sets the current line number in the source file, and, optionally, the name of the current source file. This is mainly useful if you are writing a C code generator. int main( void ) printf( "%d, %s\n", LINE, FILE ); #line 99 printf( "%d, %s\n", LINE, FILE ); #line 200 "gsharp.c" printf( "%d, %s\n", LINE, FILE ); return 0; $./a 5, adhoc.c 99, adhoc.c 200, gsharp.c file:///c /Documents%20and%20Settings/Jack%20Straub/My%...l%20Work/AdvancedC/Binders/260/140Line.html [3/29/ :12:23 AM]

26 Miscellaneous Directives #error Prints a user-define diagnostic and prevents completion of compilation. #define INSTALLATION (39) #if defined( INSTALLATION ) &&!defined( POWER ) #error "Power requirements must be specified." #endif int main( void ) return 0; $ gcc adhoc.c adhoc.c:4:2: #error "Power requirements must be specified." file:///c /Documents%20and%20Settings/Jack%20Straub/My%...%20Work/AdvancedC/Binders/260/150Error.html [3/29/ :12:23 AM]

27 Miscellaneous Directives #warning Prints a user-define diagnostic; does not prevents completion of compilation. #ifdef BIT64_ENABLED #warning "64-bit pointer issues may arise." #endif int main( void ) return 0; $ gcc adhoc.c adhoc.c:4:2: warning: "64-bit pointer issues may arise." file:///c /Documents%20and%20Settings/Jack%20Straub/My%...0Work/AdvancedC/Binders/260/160Warning.html [3/29/ :12:23 AM]

28 Miscellaneous Directives #pragma Used for compiler-dependent features. #ifdef DIGITAL_UNIX #pragma builtins #endif #pragma warning( disable : 4996 ) file:///c /Documents%20and%20Settings/Jack%20Straub/My%...20Work/AdvancedC/Binders/260/170Pragma.html [3/29/ :12:24 AM]

29 Miscellaneous Directives # The null directive; treated as a blank line (may be helpful in porting old code). file:///c /Documents%20and%20Settings/Jack%20Straub/My%...l%20Work/AdvancedC/Binders/260/180Null.html [3/29/ :12:24 AM]

CYSE 411/AIT681 Secure Software Engineering Topic #12. Secure Coding: Formatted Output

CYSE 411/AIT681 Secure Software Engineering Topic #12. Secure Coding: Formatted Output Instructor: Dr. Kun Sun 1 This lecture: [Seacord]: Chapter 6 Readings 2 Secure Coding String management Pointer Subterfuge