Thread: Error in C

Good afternoon everyone. I wanted to break the resolve of a program but I have an error and I can not fix it wanted to know your opinion about it. I'll pass the sentence and then the code for you to know I did.

Statement:
Implement strsubst without using library functions.
char * strsubst(char * s, const char * old_s, const char * new_s);

This function replaces the first occurrence of string s a old_s by new_s. The strings and old_s new_s may have different lengths. It is assumed that the memory space pointed to by s is sufficient to store the final result. The function returns the pointer s if you made the substitution s or NULL if not contains old_s.

Code:

#include <stdio.h>

char * strsubst(char * s, const char * old_s, const char * new_s)
{
char *aux=NULL;
int tamanhostring=40; // tamanho da string s;
int tamanho1=20; // tamanho da string old_s;
int i,j;

for(i=0; i <= tamanhostring; i++)
    if(s[i] == *old_s)
        *aux = i;

if(*aux)
{
for(j=0; j<tamanho1;j++)
    s[(aux-s) + j] = new_s[j];
    return (s);
}
else
return NULL;
}

int main()
  {
    char string[40],antiga[20],nova[20];

    printf("\n");
    printf("Entre com a string :");
    gets(string);
    printf("\n");
    printf("Entre com a antiga palavra :");
    gets(antiga);
    printf("\n");
    printf("Entre com a nova palavra :");
    gets(nova);
    printf("\n");
    //printf("nova string ==> %s\n",strsubst(string,antiga,nova));

    return(0);
}

Error:
Segmentation fault

Solution:
Well I've tried various solutions but can not find where the error in the main is he does not get to write the last printf is to comment so that the error must lie on the other method has changed many things but it does not. He wanted to know your opinion and what I should change my program to attain the objectives.

you should send the size of the strings as a parameter.

also in the first loop, is probably not doing what you think, you're comparing a single character, *old_s(and it is always the same), against a single character of s[i], but then you're saving i,
which is an int variable.

Code:

if(*aux)

Might this have to be, I am not certain right now; feeling sick my thinking might be effected.

Code:

if(aux)

Tim S.

The problem continues to work Segmentation fault I tried everything and any opinions of you. If you can help me and give me some opinions about my code. Thank YOu

My code is:

Code:

#include <stdio.h>

int strlen(char *s)
{
char *p = s;
while (*p != '\0')
p++;
return p - s;
}

char * strsubst(char * s, const char * old_s, const char * new_s)
{
char *aux;
char *aux1;
int i,j;
int k=0;

for(i=0; i<strlen(s); i++){
	if(s[i]==old_s[k])
		*aux1=k;
		*aux=i;
}
	while(*old_s!='\0'){
		while(*s !='\0'){
			if(s[*aux+1]==old_s[*aux1+1])
				*aux=s[*aux];	
	}
		}							

if(aux)
{
for(j=0; j<strlen(old_s);j++)
	s[(aux-s) + j] = new_s[j];
		return (s);
}
else
return NULL;
}

int main()
  {
    char string[20],antiga[7],nova[7];

    printf("\n");
    printf("Entre com a string :");
    gets(string);
    printf("\n");
    printf("Entre com a antiga palavra :");
    gets(antiga);
    printf("\n");
    printf("Entre com a nova palavra :");
    gets(nova);
    printf("\n");
    printf("nova string ==> %s\n",strsubst(string,antiga,nova));

    return(0);
    
  }

error: Segmentation Fault

No, you are not wrong.

Originally Posted by kermit

No, you are not wrong.

I read your reply too quick.. my heart sank.

After taking a deep breath, then I noticed the "not" in your reply.

I hope I'm not blowing it with the revelation... but I saw a lot of
replies without a comment on that one.

In the future with something like this, should I just observe?

Thanks Kermit!

Originally Posted by kermit

If you think you see something wrong, muck in and point it out. I think the reason why nobody mentioned it is because there is quite a bit of stuff there that isn't quite right and the code is also, IMO, somewhat confusing. If you get it wrong, someone will be sure to tell you.

Great reply! Thanks..