Thread: strstr() segmentation fault help

Hi, im new here, as well as a C programming language noob.
Also, i have a school assignment, which i dont expect it to be solved, nor a complete code, but i will need your help in understanding certain things that i completely miss.

Given a certain ficheiro.c with the following in there(example):

Code:

 #incluir "something.c"

when i run my program, i expect this to return something.c
(the name of the file prededing #incluir )
/.file2 ficheiro.c

i get the following errors:

Code:

File ficheiro.c successfully opened !!! 
1
Segmentation fault (core dumped)

the following code :

Code:

#include <stdio.h>
#include <string.h>
#define MAXLINE 1024
int main(int argc, char * argv[])
{
  int i,j,k,n;
  char *incluir="#incluir";
  char line[MAXLINE];
  char file_name[MAXLINE];
  FILE *fp;
  fp=fopen(argv[1],"r");         
  
  if(fp==NULL)                       /* if it cant open */
    printf("File cant be opened %s\n",argv[1]);    
  else
    {                              /* if it can */
      printf("File %s successfully opened !!! \n",argv[1]);  
      
      
      while(fgets(line, MAXLINE , fp))  /* copies the first line */
	{
	  printf("1\n");         /* making sure it enters the loop */
	  if(strstr(line,incluir)!= 0)	/* looks for "#incluir" in the line */		
	    {
	      printf("COOL it exists");
	      
       /* in order to copy the name of the file i must first 
	  know until where i will copy */
	      j=0; n=0;                
	      while( n<=2 )
		{
		  if(line[j] == '\"')
		    n++; 
		  j++;
		}
	      /* now int j has the position of where ' " ' is */

	      
	      /* the file *.c has in it -> #incluir "something.h" <-
		 the first ' " ', occurs at the position 9, so i
		 will start copying from 9 to j */
	      
	      for(i=9; k=0, i<j , i++; k++)		
		{
		  file_name[k]=line[i];
		}
	      file_name[k+1]='\0';    /* converting it into a string so 
					 i can read it later */
	      printf("%s \n", file_name);   
	    }       
	  else
	    {
	      printf("%s\n", line);  /* for debugging purposes */
	      printf("%s\n", incluir);
	      printf("OOPS it doesn't");	
	    }
	}
    }
  return 0;
}

when it goes into if(strstr(line,incluir)!= 0) , thats where it goes Segmentation fault, and i know it has to do with memory and for example, it happens when in an array[10], its assigned 100 chars/ints/whatever .
Please help.

strstr isn't the problem. The problem is in this loop:

Code:

j=0; n=0;                
while( n<=2 )
{
  if(line[j] == '\"')
    n++; 
  j++;
}

If you print out the value of j in this loop you'll discover that it is much larger than you think. That alone probably doesn't cause the segmentation fault because you aren't writing to memory (even though looking at memory you don't own is still undefined behavior). But when you get to this loop:

Code:

for(i=9; k=0, i<j , i++; k++)		
{
  file_name[k]=line[i];
}

j is the stopping condition for the loop, so k will definitely be higher than you want, and you will also be writing to those memory locations that you don't own. That's causing your segmentation fault.

How do you fix it? Simple. Change two things. The first loop should test for two double quotations, not 3 as you are actually testing for:

Code:

j=0; n=0;                
while( n<2 )
{
  if(line[j] == '\"')
    n++; 
  j++;
}

And the for loop is ill-formed. It is still legal, but your semicolons are misplaced, causing the loop to go longer than it should. It should be:

Code:

for(i=9, k=0; i<j; i++, k++) 
{
  file_name[k]=line[i];
}

>It still goes into segmentation fault.
This is the code I'm using to test with. It runs properly with the example file you gave.

Code:

#include <stdio.h>
#include <string.h>
#define MAXLINE 1024
int main(int argc, char * argv[])
{
  int i,j,k,n;
  char *incluir="#incluir";
  char line[MAXLINE];
  char file_name[MAXLINE];
  FILE *fp;
  fp=fopen(argv[1],"r"); 

  if(fp==NULL) /* if it cant open */
    printf("File cant open %s\n",argv[1]); 
  else
  { /* if it can */
    printf("File %s successfully opened !!! \n",argv[1]); 


    while(fgets(line, MAXLINE , fp)) /* copies the first line */
    {
      printf("1\n"); /* making sure it enters the cicle */
      if(strstr(line,incluir)!= 0) /* looks for "#incluir" in the line */ 
      {
        printf("COOL it exists");

        /* in order to copy the name of the file i must first 
        know until where i will copy */
        j=0; n=0; 
        while( n<2 )
        {
          if(line[j] == '\"')
            n++; 
          j++;
        }
        /* now int j has the position of where ' " ' is */


        /* the file *.c has in it -> #incluir "something.h" <-
        the first ' " ', occurs at the position 9, so i
        will start copying from 9 to j */

        for(i=9, k=0; i<j; i++, k++) 
        {
          file_name[k]=line[i];
        }
        file_name[k+1]='\0'; /* converting it into a string so 
                             i can read it later */
        printf("%s \n", file_name); 
      } 
      else
      {
        printf("%s\n", line); /* for debugging purposes */
        printf("%s\n", incluir);
        printf("OOPS it doesn't"); 
      }
    }
  }
  return 0;
}

Can you post the code that you're using along with the exact contents of the file you're opening? Also mention what your OS and compiler are.

>dont care about the warnings
As you wish...

>why are they undeclared?
Well, let's take a look:

>patresi.c: In function `reconhece':
>patresi.c:13: `linha' undeclared
If you look at function reconhece, you'll see that no variable called linha is declared. There is a variable called linha declared in the function apanhalinha, but that doesn't mean that reconhece can see it. The same goes for analisa.

>even with us declaring extern variables
I don't see any extern variables in the code you posted. If you want linha to be a global variable, then make it so:

Code:

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

char linha[1024];

void apanhalinha (FILE *ficheiro){ 
  (fgets(linha,1024,ficheiro));
}

void reconhece (char *mcr){
  char incluir[] = "#incluir ";
  char esquecer[] = "#esquecer ";
  char definir[] = "#definir ";
  if ((strncmp(incluir, linha, 9)) > 0)
    fazincluir(linha);
  if ((strncmp(esquecer, linha, 10)) > 0)
    fazesquecer(linha);
  if ((strncmp(definir, linha, 9)) > 0)
    fazdefinir(linha);}


void analisa(FILE *ficheiro){
  int c;
  while((c=fgetc(ficheiro)) != EOF)
    if(c == '#')
      apanhalinha(ficheiro);
  reconhece(linha);
 }

int main(int argc, char* argv[]){
  FILE *pre;
  pre = fopen (argv[1], "r");
  if (pre == NULL)
    printf("Erro: Impossivel abrir ficheiro a pre-processar\n");
  else analisa(pre);
  return 0;
}

Otherwise, you'll need to declare it in main and pass it as an argument to other functions.