CODEWITHSUNDEEP
csegmentation-fault
AlexeyMK
AlexeyMK

Reputation: 6395

Bizarre/Random Segfault in C

EDIT: Clarifying.

Warning: My C is terrible.

I've got a C program which, from the likes of it, just wants to segfault. I'll spare you the other, irrelevant details, but here's the big picture:

My code:

//...other code
printf("finished \n");   
fclose(fout);   
printf("after fclose \n");  
return 0;

The output:

finished
after fclose
Segmentation fault

I'm compiling with GCC, -std=c99.

My question:

How the heck is this even possible? What should I be looking at, that may be causing this (seemingly random) segfault? Any ideas?

Much thanks!

Upvotes: 3

Views: 4801

Answers (4)

David Harris
David Harris

Reputation: 2350

Does "Hello world!" program seg fault? If so then you have a hardware problem. If not then you have at least one problem in the code you're not showing us!

Upvotes: 1

3lectrologos
3lectrologos

Reputation: 9662

Since it's probably a stack corruption related problem, you could also use a memory debugger to locate the source of the corruption, like valgrind.
Just compile using gcc -g and then run valgrind yourprog args.

Upvotes: 2

ty.
ty.

Reputation: 11132

Compile your program with the debug flag gcc -g and run your code in gdb. You can't always trust the console to output "Segmentation fault" exactly when problematic code is executed or relative to other output. In many cases this will be misleading -- you will find debugging tools such as gdb extremely useful.

Upvotes: 0

wallyk
wallyk

Reputation: 57784

Whatever the return is going back to is causing the fault. If this code snippet is in main(), then the code has inflicted damage to the stack, most likely by exceeding the bounds of a variable. For example

int main ()
{
    int a [3];
    int j;

    for (j = 0;  j < 10;  ++j)
         a [j] = 0;
    return 0;
}

This sort of thing could cause any of a number of inexplicable symptoms, including a segfault.

Upvotes: 11

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