malloc issues

[frbowen]

I have read and read, but I cant seem to find the answer...
I have written a program that calls this function:

char *ConvertToBinaryString(Ciphertext *cipher)
{
	int i;
	char *output;

	output = (char *)malloc(sizeof(char));
	
	strcpy(output, "");

	for(i=0; i<64; i++)
	{
		if(cipher->cipher[i].bit == 1)
			strcat(output, "1");
		else
			strcat(output, "0");

	}

	return output;
}//End of ConvertToBinaryString

In my main I call the function that calls the above function twice, sequentially. The first time, the function that calls the above function executes, everthing is fine and I get the desired output. The second time I call the function that calls this function, the malloc statement at the start of this function returns a NULL. I have tried time and time again to get around this. Does anyone have any ideas?

I have tried using preset array size (the output will always be a 64 byte string), but to no avail. This function comes at the end of the function that calls it, and I have stepped through it a thousand times. Malloc always returns NULL the second time I call the function. Thanks in advance.

[frbowen]

Not sure if it makes a difference, but the structure I send the function has 64 individual bits and the purpose of the function itself is to look at the bits and create a character string of 1's and 0's.

[Guysl]

output = (char *)malloc(sizeof(char));

you have allocated a memory for a single char!
you cant use strcat on that pointer unless you allocate
enough memory to occupy that strcat.

according to your loop, it should be:
output = (char *)malloc(65*sizeof(char));

where 65 = (64 characters + 1 character for null terminator)

[bashish]

Hi,

***************************************************
output = (char *)malloc(sizeof(char));
...
strcat(output, "1");
***************************************************

How u can concat to a memory which is only one byte, u have to allocate some more memory. Looking at ur code (loop), it should be atleast 65 bytes.

ashish

[frbowen]

I agree with the previous 2 posts, but it works once without initially allocating 65 bytes. I will try it though... thanks.

[Guysl]

actually it didn't work, you just had luck (or unluck)
it didn't crashed before. you had accessed a memory
that is not belongs to you therefore one of the next scenarios
could happen:
1. your valus will be overriden
2. you override data that is in used not by you
each of these cannot be concidered as "worked"...

[frbowen]

I got it working! Thanks for everyone's input.