Thread: Pointer Problems

Hi all. So the problem im having seems apparently to be pointer related. Heres the source code.

Code:

/* squeeze: modified to remove any matching chars from string2 to string1 */#include #include #include void squeeze(char * s1 , char * s2 );int main(int argc, char **argv){	if( argc != 3 )		printf( "Usage: %s S1 S2, where any characters in S1 that are in S2 are deleted\n" , argv[ 0 ] );	else{		squeeze( argv[ 1 ] , argv[ 2 ] );	}	return 0;}void squeeze(char * s1 , char * s2 ){	int i , j , found = 0;	char * new_string = ( char * ) malloc( sizeof( char ) * strlen( s1 ) );		for( i = 0; i < strlen( s1 ); ++i){		for( j = 0; j < strlen( s2 ); ++j){			if( s1[ i ] == s2[ j ] )				++found;		}		if( !( found ) )			new_string[ i ] = s1[ i ];		found = 0;	}	printf( "%s" , new_string );}

Thanks for any help in advance!

sorry about the formatting of the source. its not letting me edit it at the moment.

Code:

/* squeeze: modified to remove any matching chars from string2 to string1 */#include #include #include void squeeze(char * s1 , char * s2 );int main(int argc, char **argv){	if( argc != 3 )		printf( "Usage: %s S1 S2, where any characters in S1 that are in S2 are deleted\n" , argv[ 0 ] );	else{		squeeze( argv[ 1 ] , argv[ 2 ] );	}	return 0;}void squeeze(char * s1 , char * s2 ){	int i , j , found = 0;	char * new_string = ( char * ) malloc( sizeof( char ) * strlen( s1 ) );		for( i = 0; i < strlen( s1 ); ++i){		for( j = 0; j < strlen( s2 ); ++j){			if( s1[ i ] == s2[ j ] )				++found;		}		if( !( found ) )			new_string[ i ] = s1[ i ];		found = 0;	}	printf( "%s" , new_string );}

wow that is not appearing as i post it. im not sure what to do.

i attached the source as a file. not sure what else to do. thanks if your willing to download and help!!

Code:

/* squeeze: modified to remove any matching chars from string2 to string1 */
#include <stdio.h>
#include <string.h>
#include <stdlib.h>

void squeeze(char * s1 , char * s2 );
int main(int argc, char **argv)
{
	if( argc != 3 )
		printf( "Usage: %s S1 S2, where any characters in S1 that are in S2 are deleted\n" , argv[ 0 ] );
	else{
		squeeze( argv[ 1 ] , argv[ 2 ] );
	}
	return 0;
}
void squeeze(char * s1 , char * s2 ){
	int i , j , found = 0;
	char * new_string = ( char * ) malloc( sizeof( char ) * strlen( s1 ) );
	
	for( i = 0; i < strlen( s1 ); ++i){
		for( j = 0; j < strlen( s2 ); ++j){
			if( s1[ i ] == s2[ j ] )
				++found;
		}
		if( !( found ) )
			new_string[ i ] = s1[ i ];
		found = 0;
	}
	printf( "%s" , new_string );
}

You need to run this through your debugger. What happens if string 1 contains multiple characters that are in string 2?

You also need to make sure your new_string is properly terminated. And you should not be casting the return value of your malloc call, and you don't need the size_of(char).

Jim

Originally Posted by jwroblewski44

i attached the source as a file. not sure what else to do. thanks if your willing to download and help!!

The problem lies with the offset of array new_string[].
Its index needs to be separate from that of s1[] or s2[].

Code:

new_string[ i ] = s1[ i ];

haha thanks everyone. @jim i tried to debug, but codelite's debugger interface was, well, buggy . im still a little hesitant on learning the cli gdb, im sure will take a lot of determination. about forgot about the null term issue thanks jim.... although im not to sure about what problem your seeing "What happens if string 1 contains multiple characters that are in string 2?"...... if any char in string1 is in string2, it wont be added. every char in string1 should checked.

and after scratching my head contemplating that the new_string needs its own offset tracker.... working on v 1.1 -- thanks itCbitC

Code:

/* squeeze: modified to remove any matching chars of string2 from string1 */
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
 
char * squeeze(char * s1 , char * s2 );
int main(int argc, char **argv)
{
    if( argc != 3 )
        printf( "Usage: %s S1 S2, where any characters in S1 that are in S2 are deleted\n" , argv[ 0 ] );
    else
        printf( "%s\n" , squeeze( argv[ 1 ] , argv[ 2 ] ) );
    return 0;
}
char * squeeze(char * s1 , char * s2 ){
    int i , j , k = 0 , found = 0;
    char * new_string = malloc( strlen( s1 + 1 ) );
     
    for( i = 0; i < strlen( s1 ); ++i){
        for( j = 0; j < strlen( s2 ); ++j){
            if( s1[ i ] == s2[ j ] )
                ++found;
        }
        if( !( found ) )
            new_string[ k++ ] = s1[ i ];
        found = 0;
    }
    new_string[ k ] = '\0';
    return new_string;
}

heres the new code. does anybody see any issues? please let me know!

Code:

char * new_string = malloc( strlen( s1 + 1 ) );

This will allocate two bytes too little.
Correct:

Code:

char *new_string = malloc(strlen(s1) + 1);

Bye, Andreas

ahh yes. Thank you very much!

Originally Posted by jwroblewski44

Code:

if ( s1[ i ] == s2[ j ] )
   ++found;

heres the new code. does anybody see any issues? please let me know!

No use iterating over s2 once a match is found. Instead terminate the search and move onto the next character in s1. So the above piece of code can be written more efficiently as:

Code:

if (s1[i] == s2[j]) {
    ++found;
    break;
}

indeed it would, and i will update it immediately.

postscript: also realized i didnt free my dynamic string, slightly suprised no one has caught my blunder yet!

Code:

/* squeeze: modified to remove any matching chars of string2 from string1 */
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
 
char * squeeze(char * s1 , char * s2 );
int main(int argc, char **argv)
{
    if( argc != 3 )
        printf( "Usage: %s S1 S2, where any characters in S1 that are in S2 are deleted\n" , argv[ 0 ] );
    else
        char * new_string = squeeze( argv[ 1 ] , argv[ 2 ] );
        printf( "%s\n" , new_string );
        free( new_string );
    return 0;
}
char * squeeze(char * s1 , char * s2 ){
    int i , j , k = 0 , found = 0;
    char * new_string = malloc( strlen( ( s1 ) + 1 ) );
     
    for( i = 0; i < strlen( s1 ); ++i){
        for( j = 0; j < strlen( s2 ); ++j){
            if( s1[ i ] == s2[ j ] ){
                ++found;
                break;
            }
        }
        if( !( found ) )
            new_string[ k++ ] = s1[ i ];
        found = 0;
    }
    new_string[ k ] = '\0';
    return new_string;
}

....thanks for scanning and showing my errors! Any more...?

one question though, does inserting that

Code:

break

into the bracketed off

Code:

if

statement cause it to exit the

Code:

for

loop when a match is found?