#include 的所有函数

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Other Standard C Functions

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abort stops the program

assert stops the program if an expression isn't true

atexit sets a function to be called when the program exits

bsearch perform a binary search

exit stop the program

getenv get enviornment information about a variable

longjmp start execution at a certain point in the program

qsort perform a quicksort

raise send a signal to the program

rand returns a pseudorandom number

setjmp set execution to start at a certain point

signal register a function as a signal handler

srand initialize the random number generator

system perform a system call

va_arg use variable length parameter lists

 


abort

Syntax:

  #include 
  void abort( void );

The function abort() terminates the current program. Depending on the implementation, the return value can indicate failure.

Related topics:

assert
atexit
exit


assert

Syntax:

  #include 
  assert( exp );

The assert() macro is used to test for errors. If exp evaluates to zero, assert() writes information to stderr and exits the program. If the macro NDEBUG is defined, the assert() macros will be ignored.

Related topics:

abort


atexit

Syntax:

  #include 
  int atexit( void (*func)(void) );

The function atexit() causes the function pointed to by func to be called when the program terminates. You can make multiple calls to atexit() (at least 32, depending on your compiler) and those functions will be called in reverse order of their establishment. The return value of atexit() is zero upon success, and non-zero on failure.

Related topics:

abort
exit


bsearch

Syntax:

  #include 
  void *bsearch( const void *key, const void *buf, size_t num, size_t size, int (*compare)(const void *, const void *) );

The bsearch() function searches buf[0] to buf[num-1] for an item that matches key, using a binary search. The function compare should return negative if its first argument is less than its second, zero if equal, and positive if greater. The items in the array buf should be in ascending order. The return value of bsearch() is a pointer to the matching item, or NULL if none is found.

Related topics:

qsort


exit

Syntax:

  #include 
  void exit( int exit_code );

The exit() function stops the program. exit_code is passed on to be the return value of the program, where usually zero indicates success and non-zero indicates an error.

Related topics:

abort
atexit
system


getenv

Syntax:

  #include 
  char *getenv( const char *name );

The function getenv() returns environmental information associated with name, and is very implementation dependent. NULL is returned if no information about name is available.

Related topics:

system


longjmp

Syntax:

  #include 
  void longjmp( jmp_buf envbuf, int status );

The function longjmp() causes the program to start executing code at the point of the last call to setjmp(). envbuf is usually set through a call to setjmp(). status becomes the return value of setjmp() and can be used to figure out where longjmp() came from. status should not be set to zero.

Related topics:

setjmp


qsort

Syntax:

  #include 
  void qsort( void *buf, size_t num, size_t size, int (*compare)(const void *, const void *) );

The qsort() function sorts buf (which contains num items, each of size size) using Quicksort. The compare function is used to compare the items in buf. compare should return negative if the first argument is less than the second, zero if they are equal, and positive if the first argument is greater than the second. qsort() sorts buf in ascending order.

Example code:

For example, the following bit of code uses qsort() to sort an array of integers:

int compare_ints( const void* a, const void* b ) {
   int* arg1 = (int*) a;
   int* arg2 = (int*) b;
   if( *arg1 < *arg2 ) return -1;
   else if( *arg1 == *arg2 ) return 0;
   else return 1;
}             

int array[] = { -2, 99, 0, -743, 2, 3, 4 };
int array_size = 7;           

...           

printf( "Before sorting: " );
for( int i = 0; i < array_size; i++ ) {
   printf( "%d ", array[i] );
}
printf( "\n" );             

qsort( array, array_size, sizeof(int), compare_ints );        

printf( "After sorting: " );
for( int i = 0; i < array_size; i++ ) {
   printf( "%d ", array[i] );
}
printf( "\n" );             

When run, this code displays the following output:

Before sorting: -2 99 0 -743 2 3 4
After sorting: -743 -2 0 2 3 4 99             

Related topics:

bsearch
(C++ Algorithms) sort


raise

Syntax:

  #include 
  int raise( int signal );

The raise() function sends the specified signal to the program. Some signals:

Signal
Meaning

SIGABRT
Termination error

SIGFPE
Floating pointer error

SIGILL
Bad instruction

SIGINT
User presed CTRL-C

SIGSEGV
Illegal memory access

SIGTERM
Terminate program

The return value is zero upon success, nonzero on failure.

Related topics:

signal


rand

Syntax:

  #include 
  int rand( void );

The function rand() returns a pseudorandom integer between zero and RAND_MAX. An example:

  srand( time(NULL) );
   for( i = 0; i < 10; i++ )
     printf( "Random number #%d: %d\n", i, rand() );         

Related topics:

srand


setjmp

Syntax:

  #include 
  int setjmp( jmp_buf envbuf );

The setjmp() function saves the system stack in envbuf for use by a later call to longjmp(). When you first call setjmp(), its return value is zero. Later, when you call longjmp(), the second argument of longjmp() is what the return value of setjmp() will be. Confused? Read about longjmp().

Related topics:

longjmp


signal

Syntax:

  #include 
  void ( *signal( int signal, void (* func) (int)) ) (int);

The signal() function sets func to be called when signal is recieved by your program. func can be a custom signal handler, or one of these macros (defined in the csignal header file):

Macro
Explanation

SIG_DFL
default signal handling

SIG_IGN
ignore the signal

Some basic signals that you can attach a signal handler to are:

Signal
Description

SIGTERM
Generic stop signal that can be caught.

SIGINT
Interrupt program, normally ctrl-c.

SIGQUIT
Interrupt program, similar to SIGINT.

SIGKILL
Stops the program. Cannot be caught.

SIGHUP
Reports a disconnected terminal.

The return value of signal() is the address of the previously defined function for this signal, or SIG_ERR is there is an error.

Example code:

The following example uses the signal() function to call an arbitrary number of functions when the user aborts the program. The functions are stored in a vector, and a single "clean-up" function calls each function in that vector of functions when the program is aborted:

void f1() {
  cout << "calling f1()..." << endl;
}              

void f2() {
  cout << "calling f2()..." << endl;
}              

typedef void(*endFunc)(void);
vector endFuncs;        

void cleanUp( int dummy ) {
  for( unsigned int i = 0; i < endFuncs.size(); i++ ) {
    endFunc f = endFuncs.at(i);
    (*f)();
  }
  exit(-1);
}              

int main() {           

  // connect various signals to our clean-up function
  signal( SIGTERM, cleanUp );
  signal( SIGINT, cleanUp );
  signal( SIGQUIT, cleanUp );
  signal( SIGHUP, cleanUp );           

  // add two specific clean-up functions to a list of functions
  endFuncs.push_back( f1 );
  endFuncs.push_back( f2 );            

  // loop until the user breaks
  while( 1 );          

  return 0;
}              

Related topics:

raise


srand

Syntax:

  #include 
  void srand( unsigned seed );

The function srand() is used to seed the random sequence generated by rand(). For any given seed, rand() will generate a specific "random" sequence over and over again.

  srand( time(NULL) );
   for( i = 0; i < 10; i++ )
     printf( "Random number #%d: %d\n", i, rand() );         

Related topics:

rand
(Standard C Date & Time) time


system

Syntax:

  #include 
  int system( const char *command );

The system() function runs the given command by passing it to the default command interpreter.

The return value is usually zero if the command executed without errors. If command is NULL, system() will test to see if there is a command interpreter available. Non-zero will be returned if there is a command interpreter available, zero if not.

Related topics:

exit
getenv


va_arg

Syntax:

  #include 
  type va_arg( va_list argptr, type );
  void va_end( va_list argptr );
  void va_start( va_list argptr, last_parm );

The va_arg() macros are used to pass a variable number of arguments to a function.

  1. First, you must have a call to va_start() passing a valid va_list and the mandatory first argument of the function. This first argument can be anything; one way to use it is to have it be an integer describing the number of parameters being passed.
  2. Next, you call va_arg() passing the va_list and the type of the argument to be returned. The return value of va_arg() is the current parameter.
  3. Repeat calls to va_arg() for however many arguments you have.
  4. Finally, a call to va_end() passing the va_list is necessary for proper cleanup.

For example:

 int sum( int num, ... ) {
    int answer = 0;
    va_list argptr;           

    va_start( argptr, num );           

    for( ; num > 0; num-- ) {
      answer += va_arg( argptr, int );
    }          

    va_end( argptr );          

    return( answer );
  }            
               

  int main( void ) {           

    int answer = sum( 4, 4, 3, 2, 1 );
    printf( "The answer is %d\n", answer );          

    return( 0 );
  }            

This code displays 10, which is 4+3+2+1.

Here is another example of variable argument function, which is a simple printing function:

void my_printf( char *format, ... ) {
   va_list argptr;            

   va_start( argptr, format );         

   while( *format != '\0' ) {
     // string
     if( *format == 's' ) {
       char* s = va_arg( argptr, char * );
       printf( "Printing a string: %s\n", s );
     }
     // character
     else if( *format == 'c' ) {
       char c = (char) va_arg( argptr, int );
       printf( "Printing a character: %c\n", c );
       break;
     }
     // integer
     else if( *format == 'd' ) {
       int d = va_arg( argptr, int );
       printf( "Printing an integer: %d\n", d );
     }         

     *format++;
   }           

   va_end( argptr );
}             
               

int main( void ) {            

   my_printf( "sdc", "This is a string", 29, 'X' );        

   return( 0 );
}             

This code displays the following output when run:

Printing a string: This is a string
Printing an integer: 29
Printing a character: X               

转载于:https://www.cnblogs.com/agpro/archive/2010/06/11/1756420.html

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