segmentation fault error

vermin1302 · #1 24-Feb-2006, 21:50

Ok, this code compiles just fine, but once I run the program and move into this section of it, I get a segmentation fault. Since I'm not really much of a programmer (this is the first thing I've written in five years), I'm not quite sure what's going wrong.

Here's the snippet that's giving me trouble:

CPP / C++ / C Code:

    else {
    #ifndef _WIN32
    system("/usr/bin/clear");
    #else
    system("cls");
    #endif
    
    int old_turn;
    int old_ps;
    int old_pa;
    int old_cs;
    int old_ca;
    
    printf("Displaying formatted contents of dilemma.log.\n\n");
    printf("| TURNS | PSCORE | PAVG | CSCORE | CAVG |\n");
    printf("|-------+--------+------+--------+------+\n");
    
    while(fscanf(pFile,"%3d %3d %4f %3d %4f",old_turn,old_ps,old_pa,old_cs,old_ca) != EOF)
    {
         printf("|  %03d  |  %03d   | %4.2f |  %03d   | %4.2f |\n",old_turn,old_ps,old_pa,old_cs,old_ca);
         printf("|-------+--------+------+--------+------+\n");
    }
    
    printf("\nEnd of file reached.\n");
    printf("Press any key to return.\n");
    tempvar = getch();
    
    break;
    }

Here's the information from the error message:

AppName: dilemma.exe AppVer: 3.2.0.9 ModName: ntdll.dll
ModVer: 5.1.2600.2180 Offset: 00001010

Thanks a bunch for any help!

Chris.Dev · #2 24-Feb-2006, 22:45

The most likely reason for the segmentation fault is demonstrated bellow.

Try compiling and running this code:

CPP / C++ / C Code:

#include <stdio.h>

/* ^^^^^ im assuming this is C? ^^^^^ */

int main(void) {
    int i1, i2, i3, i4;        /* some integers to be read from FILE *fp */
    FILE *fp;                /* input file pointer */


    fp = NULL;              /* fp = NULL?! UhOh, a stack dump waiting to
                                    happen!
                                */
                              
    /* ready for the segmentation fault? */
    fscanf(fp, "%d%d%d%d", i1, i2, i3, i4);
    /************************************/
    
    return 0;
}

Passing a NULL pointer to a standard library function is never a good idea, and will never give the results you want.

simple solution:

CPP / C++ / C Code:


    if(pFile == NULL) {
        printf("ERROR: pFile is an invalid file pointer: %p !\n", pFile);
        break;        /* or whatever else you want to do */
    }

The real problem here however is that your file pointer was never assigned a value:

fopen return value:

Quote:

Originally Posted by cplusplus.com

Return Value:
If the file has been succesfully opened the function will return a pointer to the file. Otherwise a NULL pointer is returned.

If your program hadn't crashed it still wouldn't have worked right anyway so make sure you are accessing a valid file.

One more thing...

Quote:

Originally Posted by vermin1302

#ifndef _WIN32
system("/usr/bin/clear");
#else
system("cls");
#endif

Is that really what you wanted to do?

cls is for windows
clear is for *nix

vermin1302 · #3 24-Feb-2006, 23:16

CPP / C++ / C Code:

#ifndef _WIN32
system("/usr/bin/clear");
#else
system("cls");
#endif

That actually says...if it's NOT a windows machine, use clear.
If it is, use cls.

But, as far as the suggestion you gave...maybe it would help if I added a larger sample of that problematic code snippet here:

CPP / C++ / C Code:

case 'V':                             // player wants to view logs
    {
    pFile = fopen("dilemma.log","r");
    
    if(pFile=NULL) {
    perror("Error opening dilemma.log");
    printf("\nCheck that it exists and try again.\n");
    printf("Press any key to continue.\n");
    tempvar = getch();
    
    break;
    }
    else {
    #ifndef _WIN32
    system("/usr/bin/clear");
    #else
    system("cls");
    #endif
    
    int old_turn;
    int old_ps;
    int old_pa;
    int old_cs;
    int old_ca;
    
    printf("Displaying formatted contents of dilemma.log.\n\n");
    printf("| TURNS | PSCORE | PAVG | CSCORE | CAVG |\n");
    printf("|-------+--------+------+--------+------+\n");
    
    while(fscanf(pFile,"%3d %3d %4f %3d %4f",old_turn,old_ps,old_pa,old_cs,old_ca) != EOF)
    {
         printf("|  %03d  |  %03d   | %4.2f |  %03d   | %4.2f |\n",old_turn,old_ps,old_pa,old_cs,old_ca);
         printf("|-------+--------+------+--------+------+\n");
    }
    
    printf("\nEnd of file reached.\n");
    printf("Press any key to return.\n");
    tempvar = getch();
    
    break;
    }
    break;
    }

maybe that'll make the problem easier to solve.

As you can see, I did use fopen() to assign a value to my file pointer (pFile), and I also did account for a NULL pointer.

The heading there in the else statement (right before the while) will print out and then the segmentation fault happens right afterward.

TreyAU21 · #4 25-Feb-2006, 00:58

fscanf(FILE * stream , const char * format [ , argument , ...] );

You aren't using pointers as your arguments in fscanf().

Here is your code:

CPP / C++ / C Code:

while(fscanf(pFile,"%3d %3d %4f %3d %4f",old_turn,old_ps,old_pa,old_cs,old_ca) != EOF)

add the & sign in front of the variables in fscanf to reference the address of the variables...

CPP / C++ / C Code:

while(fscanf(pFile,"%3d %3d %4f %3d %4f",&old_turn,&old_ps,&old_pa,&old_cs,&old_ca) != EOF)

That should fix it I think.

Chris.Dev · #5 25-Feb-2006, 01:29

Quote:

Originally Posted by vermin1302

CPP / C++ / C Code:

#ifndef _WIN32
system("/usr/bin/clear");
#else
system("cls");
#endif

My bad, sorry it's real late here and im munching caffeine pills working on a project

I read it as #ifdef, I guess I need some sleep

Anyway TreyAU21 is right, you need to pass your variables by referance.
I also overlooked that :-/

This situation should highlight the reasons not to use scanf or it's dirivitives

vermin1302 · #6 25-Feb-2006, 11:45

Thanks again, but that still didn't fix the problem.

I changed the while line so it now reads

CPP / C++ / C Code:

    while(fscanf(pFile,"%3d %3d %4f %3d %4f",&old_turn,&old_ps,&old_pa,&old_cs,&old_ca) != EOF)

Compiles fine again, gets to the same spot and faults.

vermin1302 · #7 25-Feb-2006, 11:48

oooh, looks like I found the source of the problem.

I had

CPP / C++ / C Code:

if(pFile = NULL)

When I changed it to

CPP / C++ / C Code:

if(pFile == NULL)

, it stopped faulting.

However, now the actuall log output is messed up.

When I run the program, here's what I get:

Quote:

Displaying formatted contents of dilemma.log.

| TURNS | PSCORE | PAVG | CSCORE | CAVG |
|-------+--------+------+--------+------+
| 90 | 270 | 0.00 | 1077936128 | 0.00 |
|-------+--------+------+--------+------+
| 54 | 162 | 0.00 | 1077936128 | 0.00 |
|-------+--------+------+--------+------+

End of file reached.
Press any key to return.

The contents of the logfile are:

90 270 3.00 270 3.00
54 162 3.00 162 3.00

vermin1302 · #8 25-Feb-2006, 13:38

Ok, I figured out what was wrong. I declared old_ca and old_pa as int instead of float. It's all fixed and working fine now.

Thanks a lot for your help!

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