First debugging - Segmentation fault

Hi dear friends,
I have problem including Segmentation fault and I don't know how to repair it. I am using gdb but I haven't knowledge how to repair mistake like this:

Code:

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Program received signal SIGSEGV, Segmentation fault.
0xb7e66021 in _IO_vfscanf_internal (s=s@entry=0x804b008, format=format@entry=0x8048d89 "%s", argptr=argptr@entry=0xbffca388 " ", errp=errp@entry=0x0) at vfscanf.c:1095
1095    vfscanf.c: No such file or directory.
(gdb)

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I think so this mistake means so I filled much memory but I don't know, how could I make it correctly. Can you help me please? Should I share my code?

Thank you, greetings Tomas.

Use "bt" (backtrace) to find out where, in your code, the problem happened.

It looks like you're passing an invalid value to scanf() (or related function), though. Hard to say without seeing code.

It gave me this:

Code:

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#0  0xb7e66021 in _IO_vfscanf_internal  (s=s@entry=0x804b008, format=format@entry=0x8048d89 "%s",  argptr=argptr@entry=0xbffca388 " ", errp=errp@entry=0x0) at  vfscanf.c:1095
#1  0xb7e6d607 in __isoc99_fscanf (stream=0x804b008, format=0x8048d89 "%s") at isoc99_fscanf.c:34
#2  0x08048906 in main () at main.c:65

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Quote:

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Originally Posted by maestorm

It gave me this:

Code:

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#0  0xb7e66021 in _IO_vfscanf_internal  (s=s@entry=0x804b008, format=format@entry=0x8048d89 "%s",  argptr=argptr@entry=0xbffca388 " ", errp=errp@entry=0x0) at  vfscanf.c:1095
#1  0xb7e6d607 in __isoc99_fscanf (stream=0x804b008, format=0x8048d89 "%s") at isoc99_fscanf.c:34
#2  0x08048906 in main () at main.c:65

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Please show us main.c. The problem seems to be related to line 65 of that file. Need to see that line and any related variable definitions.

Here is part of code and thank you for your help, really thank you.

Code:

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do
 60    {
 61        c = fgetc(fr);
 62        if(isalpha(c))
 63        {
 64                fseek(fr, -1, SEEK_CUR);        //zjisti ze je tam alfabet. znak, posune se zpet a nacte slovo
 65                fscanf(fr, "%s", s[cisloSlova].cele);
 66                upravSlovo(s[cisloSlova].cele);
 67                int length = strlen(s[cisloSlova].cele);
 68                if(length>5) {
 69                    //if(CompFunc(s[cisloSlova].cele) == true) {
 70                        fprintf(fh, "%d " , cisloSlova);
 71                        fprintf(fh, "%s\n" , s[cisloSlova].cele);
 72                        //printf("\n%d: %s", cisloSlova, s[cisloSlova].cele);
 73
 74                    //}
 75                }
 76                cisloSlova++;
 77        }
 78
 79    }while(feof(fr)==0);
 80
 81    fclose(fr);
 82    fclose(fh);

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> fscanf(fr, "%s", s[cisloSlova].cele);
How is s declared?
What is the current value of cisloSlova? (ask the debugger)
How is the cele member declared?

s is declared: Slovo s[6000];
int cisloSlova = 0; //initialization and after it is incremented for every word
char cele[21]; //in structure on begin

Quote:

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Originally Posted by maestorm

s is declared: Slovo s[6000];
int cisloSlova = 0; //initialization and after it is incremented for every word
char cele[21]; //in structure on begin

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What is the structure of struct Slovo? How are the members defined?

Here is whole code, but still some parts I am working on..

Code:

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

typedef struct
{
    char cele[21];
    int pocet;
    char a;
    char b;
    int length;
}Slovo;

void upravSlovo(char*);
void vstupString(char*);
//bool CompFunc(char*);

int main(void) {

    Slovo s[6000];
    int cisloSlova = 0;

    char c;


    printf("\nPress any key");
    getchar();

    FILE *fr;
    fr = fopen("file.txt", "r");

    FILE *fh;
    fh = fopen("helper.txt", "a+w");

    int celkovaDelka = 0;
    do
    {
        c = fgetc(fr);
        celkovaDelka++;
    }while(feof(fr)==0);

    char *obsah;
    obsah = (char*)malloc(celkovaDelka);

    rewind(fr);

    int i = 0;
    do
    {
        c = fgetc(fr);
        obsah[i] = c;
        i++;
    }while(feof(fr)==0);

    rewind(fr);
   
    do
    {
        c = fgetc(fr);
        if(isalpha(c))
        {
                fseek(fr, -1, SEEK_CUR);        //zjisti ze je tam alfabet. znak, posune se zpet a nacte slovo
                fscanf(fr, "%s", s[cisloSlova].cele);
                upravSlovo(s[cisloSlova].cele);
                int length = strlen(s[cisloSlova].cele);
                if(length>5) {
                    //if(CompFunc(s[cisloSlova].cele) == true) {
                        fprintf(fh, "%d " , cisloSlova);
                        fprintf(fh, "%s\n" , s[cisloSlova].cele);
                        //printf("\n%d: %s", cisloSlova, s[cisloSlova].cele);

                    //}
                }
                cisloSlova++;
        }

    }while(feof(fr)==0);

    fclose(fr);
    fclose(fh);

    int pocetSlov = cisloSlova;

    int o;
    for(o=0;o<pocetSlov-1;o++) s[o].pocet = 1;
    for(o=0;o<pocetSlov-1;o++)
    {   
        for(i=pocetSlov-1;i>0;i--)
        {
            if(s[o].cele!=s[i].cele)
            {
                if(strcmp(s[o].cele, s[i].cele)==0)
                {
                    s[o].pocet++;
                }
            }

        }
        printf("\n %s: %d",s[o].cele , s[o].pocet);
    }
    Slovo max[10];
    max[0].pocet = 1;
    int maximum = 1;
    i = 0;

    char *maximalniSlovo;


        for(o=0;o<pocetSlov-1;o++)
        {
            if(s[o].pocet>maximum)
            {
                maximum = s[o].pocet;
                maximalniSlovo = s[o].cele;
                max[0].pocet = maximum;
            }
        }


        printf("\n Slovo s maximalnim vyskytem %d - %s", max[0].pocet, maximalniSlovo);

    free(obsah);
    return 0;
}

void upravSlovo(char *verb)
{
    bool upraveno = false;
    do
    {
        if(isalpha(verb[strlen(verb)-1]))
        {
            upraveno = true;
        }
        else
        {
            verb[strlen(verb)-1] = '\0';
        }
    }while(upraveno==false);


}

void vstupString(char *verb)
{

    if(fgets(verb, 20, stdin)!=NULL)
    {
        char *p = strchr(verb, '\n');
        if(p!=NULL) *p = '\0';
    }

}

/*bool CompFunc(char *verb) { // Použít rekurzi
int i = 0;
char array[i];
for(;i<=2;i++) {
   
}
return bool;
}
*/

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Quote:

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Here is whole code, but still some parts I am working on..

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You would also need to provide the two files specified in the code. It may or may not have an effect on the seg fault, but we should have the whole package.

So why haven't you used the debugger yet?

You've caught a segfault, but then what?

Type
frame 2
to get to main - presumably line 65 still.

Type
print cisloSlova
to see if you're out of bounds of your array.

It gave me this:

Code:

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(gdb) run
Starting program: /home/maestorm/fi.muni/C_programming/files/dutomas/a.out

Press any key

Program received signal SIGSEGV, Segmentation fault.
0xb7e66021 in _IO_vfscanf_internal (s=s@entry=0x804b008, format=format@entry=0x8048d89 "%s", argptr=argptr@entry=0xbffca388 " ", errp=errp@entry=0x0) at vfscanf.c:1095
1095    vfscanf.c: No such file or directory.
(gdb) frame 2
#2  0x08048906 in main () at main.c:65
65                    fscanf(fr, "%s", s[cisloSlova].cele);
(gdb) print cisloSlova
$1 = 6108
(gdb)

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Maybe this is not the source of your problem, but I noticed that your didn't check for NULL pointers when opening files, nor when allocating dynamic memory. Just trying to guess, here... maybe you are making use of any NULL pointers when calling any file related standard functions? Or maybe you are using any NULL pointers supposed to point to any non-existent space in dynamic memory?

Code:

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FILE *fr;
fr = fopen("file.txt", "r");
/* if (fr == NULL ) { printf("Unavailable file."); return 0; } */

FILE *fh;
fh = fopen("helper.txt", "a+w");
/* if (fh == NULL ) { printf("Unavailable file."); return 0; } */

/* skipped portions of your code */

char *obsah;
obsah = (char*)malloc(celkovaDelka);
/* if (obsah == NULL ) { printf("Unable to allocate memory."); return 0; }  */

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Quote:

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Originally Posted by maestorm

Code:

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(gdb) print cisloSlova
$1 = 6108
(gdb)

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There is the cause of the crash. Your code is modifying element 6108 of an array with 6000 elements.

Now you need to work out why that variable is getting a value of 6108.

Two obvious things you need to look at.

1) Check all operations on the file (fseek(), reading, etc) to see if they succeed. Your code doesn't check, but then proceeds as if every read succeeds. That is dangerous.
2) Your upravSlovo() function will use negative indices to access array elements if supplied input with no alphabetic characters - which is possible if a read operation fails (given that your code proceeds anyway). That gives undefined behaviour.

As a general comment, it is a really bad idea to mix usage of fseek() and fscanf() on the same file.