why glibc detected *** double free or corruption (out): 0x0000002ab292b110

[zcrself]

struct window
{
       int chrNum;
       int csID;
       char *indicInd;
       char *japInd;
       int startPos;
       int endPos;
};

int main(int argc,char *argv[])
{
    struct window *w = (struct window *) malloc (30);
    struct window *tmpW;
    tmpW   = wInd; 
    
    /*
    assign values to (struct window *) w
    */
    
    free(w);
    
    return 0;
}

run result:
glibc detected *** double free or corruption (out): 0x0000002ab292b110

[Memloop]

You can't assume anything about the size of the struct, so this is wrong on so many levels:

malloc(30)

Also, don't cast the return value of malloc in C code. You should also check if the call to malloc is successful or not.

[Salem]

You also seem to be assuming that the code you commented out wasn't part of the problem.

[zcrself]

You can't assume anything about the size of the struct, so this is wrong on so many levels:

malloc(30)

Also, don't cast the return value of malloc in C code. You should also check if the call to malloc is successful or not.

how to malloc memory?
malloc(30*sizeof(struct)) ; ?

[abhijitdhopate]

First question:
Why you use malloc(30). From where this 30 comes. Considering 32 bit machine you would have use 24.
On all top of that this method is wrong...!!!
I will suggest following way.
struct win some_name; // Declare a struct variable
w = malloc (sizeof (some_name);
if ( W == NULL)
Exit with error code
else
continue ;[/I][/I][/I]
free (w) ;
Please fell free to point errors

[iMalc]

Don't you think that if you had to calculate the size of a struct yourself (which is rather tedious and error prone), that they'd make a way of doing it automatically in the language instead?
Guess what? They did! it's called "sizeof"

    struct window *w = malloc(sizeof(*w));

How cool is that!

You know what else? That's probably not the cause of the "double free or corruption" problem you're having. You need to post code that actually compiles and produces the error. Don't make up mock examples that don't actually produce the problem at all. The bug is never in the bit you think it's in, or you'd have already solved it.

[zcrself]

Don't you think that if you had to calculate the size of a struct yourself (which is rather tedious and error prone), that they'd make a way of doing it automatically in the language instead?
Guess what? They did! it's called "sizeof"

    struct window *w = malloc(sizeof(*w));

How cool is that!

You know what else? That's probably not the cause of the "double free or corruption" problem you're having. You need to post code that actually compiles and produces the error. Don't make up mock examples that don't actually produce the problem at all. The bug is never in the bit you think it's in, or you'd have already solved it.

Your guess is right! Because my codes is long very much, so I make up this example。 I have thougt error was in it.

I have solved this error. Thans everyone for helps!

[_Mike]

    struct window *w = malloc(sizeof(*w));

Dereferencing an uninitialized pointer? Isn't that kinda unsafe?

[EVOEx]

Dereferencing an uninitialized pointer? Isn't that kinda unsafe?

If you'd do anything with it, yes. Not if you simply pass it to sizeof, which doesn't even dereferences it but rather finds out the type of the dereferenced pointer. Although I usually use sizeof(type), because I prefer that readability.

[_Mike]

Ah yes you are right. I did some tests and it seems sizeof() is evaluted at compile time. I had incorrectly assumed it was done at runtime.

[quzah]

Ah yes you are right. I did some tests and it seems sizeof() is evaluted at compile time. I had incorrectly assumed it was done at runtime.

It depends on what you use it on. C99 thwarts that concept by adding variable length arrays.


Quzah.

[MK27]

Didn't know that was specific to C99. Anyway, eg:

#include <stdio.h>

void test(int len) {
	int ray[len];	/* runtime value */
	printf("-> %d ints = %lu bytes",len,sizeof(ray));
}


int main() {
	int n;
	scanf("%d",&n);
	test(n);
	return 0;  
}