Standard C Library - 思维火花 - 博客频道 - CSDN.NET
The return value of signal() is the address of the previously defined function for this signal, or SIG_ERR is there is an
error.
srand
Syntax:#include <stdlib.h>
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(), time().
system
Syntax:#include <stdlib.h>
int system( const char *command );The system() function runs the given command as a system call. 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(),
va_arg
Syntax:#include <stdarg.h>
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 describes 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, ... );
int main( void ) {
int answer = sum( 4, 4, 3, 2, 1 );
printf( "The answer is %d/n", answer );
return( 0 );
}
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 );
}This code displays 10, which is 4+3+2+1.
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