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Old 03-23-2006, 11:48 AM   #1
Registered: Nov 2003
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SIGSEGV when running an executable in a loop

Hi friends,

I have a shell script that runs an executable in a 'while' loop. The programs are in C. The executable is run around 100 times in the loop and different parameters are passed to the program each time. I used to get segementation fault more often than not when running this script. Later found out that there is a 'char *' variable to which a string of more than 1 byte is copied. When i changed this to a char array of 10, this problem seem to have disappeared. anybody has any idea why this happened?

Thanks for any suggestions.
Old 03-23-2006, 12:37 PM   #2
Registered: Jul 2004
Location: USA
Distribution: Fedora 9, LFS 6.3, Unbuntu 8.04, Slax 6.0.7
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Is the question Why you program seg faulted?

If that is the case the reason might be if you have a char* and you don't do a new there is no space to store the value you are coping to the char*. Since you changed it to a char[10] when the program starts that array is given enough memory space to store 10 characters. You could have done the same thing by doing this

char* myChar;
myChar = new char[10];

that will create a memory location to store 10 characters.

Hope that was the question.
Old 03-23-2006, 02:23 PM   #3
Registered: Nov 2003
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Yes, that was my question. but i know why it seg faulted, because there was not enough space. but i want know how using a 'char *' is causing SIGSEGV in the loop, since all the invocations of the executable have its own memory space?
Old 03-23-2006, 05:01 PM   #4
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When you have a table, you have memory to copy the string. If you just have char *, there's no space (what's more, you have it uninitialized, so it points to some random address). When you try to copy to space that doesn't exist...
Old 03-23-2006, 05:05 PM   #5
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They have there own memory space but was your pointers pointing at the memory?

The char* points to a memory location, when first created it points at a random location, ( basically what the value was at its location when it was created ). It this value is outsidde your memory SIGSEGV.

When you set it as an array, 10 bytes where allocated and the char* was set to point to the first of them. The same as if you did new char[10]; So its now poiting at the programs allowed memory.

Its all to do with initializing your pointers, and knowing where their pointing.
Old 03-24-2006, 12:09 PM   #6
Registered: Nov 2003
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i get it, thanks a lot for the replies guys.


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