Programming Forums > Application Development > C++

tempest · May 28th, 2005, 12:41 AM

In the very beginnings of an encryption program i'm running into an error reallocating memory for a character array... whenever i give it an argument via command-line, i get a segmentation fault.

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 #include <iostream>
 #include <math.h>
 
 char *msg = "I like to encrypt things!";
 
 int main(int argc, char *argv[]) {
 	if(argc == 2) {
 		free(msg);
 		msg = (char *)malloc(sizeof(argv[1]));
 		strcpy(msg, argv[1]);
 	}
 
 	printf("%s\n", msg);
 	return 0;
 }

Ooble · May 28th, 2005, 6:59 AM

First of all, stick a printf() before and after every single statement, and find out which line's buggered. Then post back.

Nuticulus · May 28th, 2005, 7:08 AM

You cannot free that memory pointed to by msg! It has not been allocated by malloc, calloc or realloc, and you cannot free it! That is where your segmentation fault comes from.

Ooble · May 28th, 2005, 7:26 AM

That's what I was thinking, but I wasn't sure. You have to allocate memory manually before you can deallocate it.

May 28th, 2005, 12:41 AM	#1
tempest Programming Guru Join Date: Oct 2004 Posts: 1,041 Rep Power: 5	A dreaded "segmentation fault" error :( In the very beginnings of an encryption program i'm running into an error reallocating memory for a character array... whenever i give it an argument via command-line, i get a segmentation fault. (Toggle Plain Text) #include <iostream> #include <math.h> char msg = "I like to encrypt things!"; int main(int argc, char argv[]) { if(argc == 2) { free(msg); msg = (char )malloc(sizeof(argv[1])); strcpy(msg, argv[1]); } printf("%s\n", msg); return 0; } #include <iostream> #include <math.h> char msg = "I like to encrypt things!"; int main(int argc, char argv[]) { if(argc == 2) { free(msg); msg = (char )malloc(sizeof(argv[1])); strcpy(msg, argv[1]); } printf("%s\n", msg); return 0; } __________________

May 28th, 2005, 6:59 AM	#2
Ooble I eat cake for breakfast. Join Date: Jul 2004 Location: In my box. Posts: 4,434 Rep Power: 9	First of all, stick a printf() before and after every single statement, and find out which line's buggered. Then post back. __________________ Me :: You :: Them

May 28th, 2005, 7:08 AM	#3
Nuticulus Programmer Join Date: May 2005 Location: England Posts: 61 Rep Power: 4	You cannot free that memory pointed to by msg! It has not been allocated by malloc, calloc or realloc, and you cannot free it! That is where your segmentation fault comes from. __________________ http://www.nuticulus.net/hackmysig/sig.PNG Give my site a chance, you know you want to ;-) Google will solve 99% of your problems. Including those with your sex life. Caution, may <strike>contain</strike> be nuts.

May 28th, 2005, 7:26 AM	#4
Ooble I eat cake for breakfast. Join Date: Jul 2004 Location: In my box. Posts: 4,434 Rep Power: 9	That's what I was thinking, but I wasn't sure. You have to allocate memory manually before you can deallocate it. __________________ Me :: You :: Them

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Programming Forums > Application Development > C++

A dreaded "segmentation fault" error :(