Thread: easy problem with strchr-clone

Hi,
i have some questions/problems with the following snippet:

Code:

char *strchr( const char *str, int c )
{
	char *buf = ( char* )malloc( strlen( str ) );
	while( *str )
	{
		if( *str == c )
		{
			while( *str )
				*buf++ = *str++;
			*buf = 0;
			return buf;
		}
	*str++;
	}
	return NULL;
}

Why will

Code:

    char *text = "hello world!";
    char *new = strchr( text, 'w' );

...return NULL? And why will

Code:

    char *text = "hello world!";
    char *new = strchr( text, CHAR_THAT_DOESNT_OCCUR_IN_STRING );

...crash??
Please help me... (with the problem/mistake, no style flames >:( )
Thanks in advance,
bye.

Mostly, you're returning the wrong thing - a modified buf

Code:

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

char *my_strchr( const char *str, int c )
{
    while ( *str )
    {
        if ( *str == c )
        {
            // only malloc if we actually copy something
            char *buf = malloc( strlen( str ) + 1 );    // forgot the +1
            char *temp = buf;                           // buf is returned, dont change it
            while ( *str )
                *temp++ = *str++;
            *temp = 0;
            return buf;
        }
        str++;
    }
    return NULL;
}


int main ( ) {
    char *text = "hello world!";
    char *new;
    
    new = my_strchr( text, 'w' );
    printf( "%p %s\n", new, new ? new : "(null)" );
    new = my_strchr( text, 'z' );
    printf( "%p %s\n", new, new ? new : "(null)" );

    return 0;
}

strchr, as defined by ANSI, should only return the pointer to the first occurance of the character in the string and not the position of that character in a newly allocated string.

You don't need to use any additional memory for the string: trying to do simply makes the problem more difficult than it needs to be.

Try again, but this time return a pointer within the same string as the one passed by the caller! Good luck!

Ian Woods