Thread: Unsolved Segmentation Fault

File opens fine. I've written to it before. In fact, I've run the program before and had no trouble. I made a few changes to it though and thats when it started bugging out. Unfortunately I do not have an earlier version of the file. Anyone have a suggestion for the best lite linux C debugger?

I don't know about "lite" debuggers, but GDB is an amazing tool. Not too hard to do a basic run. Compile your code with the -g flag, then load the executable into gdb and run it. When it crashes, get a backtrace.

Code:

$ gcc -g -Wall -o foo foo.c
$ gdb foo
(gdb) r
Program received SIGSEGV (or something like that)
(gdb) bt
A bunch of useful information about the state of the program and function stack when it crashed.

Originally Posted by anduril462

I don't know about "lite" debuggers, but GDB is an amazing tool. Not too hard to do a basic run. Compile your code with the -g flag, then load the executable into gdb and run it. When it crashes, get a backtrace.

Code:

$ gcc -g -Wall -o foo foo.c
$ gdb foo
(gdb) r
Program received SIGSEGV (or something like that)
(gdb) bt
A bunch of useful information about the state of the program and function stack when it crashed.

To add to this; If you prefer a graphical frontend there's DDD - Data Display Debugger - GNU Project - Free Software Foundation (FSF)
It has it's quirks and it's not as easy to use as using gdb directly in my opinion, but if you need to watch a lot of variables while stepping through the code it gives a much better overview than gdb*

*) Or it could just be me not knowing how to use gdb effectively

Anduril, thanks for the suggestion. I've got to look at gdb documentation to learn to use it a little better, but it seems like this will be great help.

CommonTater, I'm making sure to use backups now. Ctr-Z did wonders though, I was able redo to my stable version. Rebuilding will hopefully avoid the fault. Also, I do need to start adding more error checking into my code. Thanks for the suggestions.

Laserlight, I'm going to take a look at version control systems. This seems like it will be extremely helpful!

_Mike, if I don't like gdb I will take a look at DDD. I have to figure out what environment and software support I like for C. I've got to build a good base for getting out of C beginnerville.

So, I went back to my last working version of the program, then i went through and changed some values of arrays, but I incremented them all by the same amount so it should work the same way. Of course, a segmentation fault occurs at the beginning of the program.

Here is my main:

Code:

int main(){
	//printf("main start\n");
	struct hostfreq hostCon[1000001];
	//printf("host con built\n");
	int i = 0;
	while(i<=1000000){
		hostCon[i].freq=0;
		i++;
	}
	addHosts(hostCon);
	i = 0;
	//printf("before copy\n");
	sort(hostCon);
	/*for(i; i<=1999; i++){
		printf("Host name %s : %i \n i is %i\n", hostCon[i].hostName, hostCon[i].freq, i);
	}*/
	//printf("program complete\n");
	return 0;

}

The gdb output looks like this:

Code:

Starting program: ***/host 

Program received signal SIGSEGV, Segmentation fault.
0x08048a4d in main () at hostanalysis.c:145
145			hostCon[i].freq=0;

the structure code looks like this:

Code:

struct hostfreq{
	int freq;
	char hostName[255];
};

Any suggestions? Thanks

Originally Posted by quzah

Your compiler is not a fan of making 247mb arrays.
Quzah.

Especially not on the program's stack, which is usually about a megabyte.

Our friend needs to learn how to A) minimize data structures and B) use malloc() and free().