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Old 12-30-2006, 02:56 PM   #1
PatrickNew
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Immediate Segmentation Fault


I'm writing an application that reads in a text file containing only the chars '0' and '1', and then writes the associated binary file. My trouble is, although my code compiles without so much as a warning, running it produces an immediate segmentation fault. (Segmentation Fault: The program recieved signal 11 SIGSEV). Debugging with printf statements (btw, it's written in C) confirms that it never even executes the first line of main().

Is it possible that such a problem is caused by faulty code (There is a lot of pointer usage which might cause a segmentation fault) if the first line is never executed? Should I look at my gcc? This gcc has served me quite well in the past, so I hesitate to suspect it, but I'm still confused.

If it's a code problem, how does one debug a program that won't even start in gdb?
 
Old 12-30-2006, 03:02 PM   #2
slzckboy
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do a
[code]
gdb prog_name

then do
Code:
 
run [args]
after seg fault do bt

then post output here so we can have a look_c.
 
Old 12-30-2006, 03:15 PM   #3
traene
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Sounds strange. Try to isolate the problem by divide and conquer. main should look like:

Code:
int main(int argc, const char** argv) {
    ...
}
Do you use multiple files? How do you produce your binary?
 
Old 12-30-2006, 03:17 PM   #4
Mara
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There are situations when the code crashes so fast, that printf is not yet shown. Check it with gdb, like one of the previous posters suggests.
 
Old 12-30-2006, 03:20 PM   #5
slzckboy
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sorry i didn't see the bit where u said it will not even start in gdb.

....

is it worth trying to start it in valgrind ?
how is the file that the program reads from made?
 
Old 12-30-2006, 03:32 PM   #6
Mara
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What does it mean that it doesn't start in gdb? What's the error you get (in gdb)?
 
Old 12-30-2006, 03:40 PM   #7
PatrickNew
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Well, I feel silly, I found the error. Aparently it was just crashing so fast printf didn't register yet. It was on like the 3rd line of code. I incorrectly used strcat. I didn't realize strcat didn't just return the two arguments concatenated, it actually altered the first argument. Aparently argv[1] didn't appreciated being written to. Sorry and thanks!
 
Old 12-31-2006, 03:27 PM   #8
ta0kira
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The thing about Linux programs with standard output is that if the program crashes before the buffer is cleared then the output sitting there isn't shown. For this reason I use test output lines and immediately flush the output buffer (e.g. 'std::cout << "tag1\n"; std::cout.flush();'.) This lets me know the last test line to be executed and keeps the buffer from being erased before display.
ta0kira
 
Old 12-31-2006, 03:38 PM   #9
slzckboy
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there is no such facility in straight C for that is there ??!??

cheers
 
Old 12-31-2006, 03:40 PM   #10
raskin
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fflush
<the above must have been the only 6 characters of reply, but it's too short>
 
Old 12-31-2006, 03:45 PM   #11
slzckboy
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learn something every day..
 
  


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