strcat_ex.c

#include <stdio.h>
#include <stdlib.h>
#include <stdarg.h>
#include <string.h>

char * strcat_ex( const char *s, ... )
{    
    if ( s == NULL ) {
        return NULL;
    }
    
    va_list ap;
    
    size_t n = 0;
    
    va_start( ap, s );
    for ( const char *p = s; p != NULL; p = va_arg( ap, const char * ) )
    {
        n += strlen( p );
    }
    va_end( ap );
    
    ++n;
    char *result = malloc( n );
    if ( result == NULL ) {
        return NULL;
    }
    
    n = 0;
    va_start( ap, s );    
    for ( const char *p = s; p != NULL; p = va_arg( ap, const char * ) )
    {
        strcpy( result + n, p );
        n += strlen( p );
    }
    va_end( ap );
    
    return result;
}