#include <memory.h> //我试了一下，C语言这么用，C++还可以用<cstring> 
#include <stdio.h>

int main( void ) 
{ 
    char buffer[] = "This is a test of the memset function"; 
    printf( "Before: %s\n", buffer );

    memset( buffer, '*', 4 );
    printf( "After: %s\n", buffer );

    memset( buffer, '*', sizeof(buffer) );
    printf( "After: %s\n", buffer );
    return 0;
}