Thread: pointer question

my program kept crashing for some reason and i narrowed it down to the following code (i know it has something to do with the pointer):

Code:

struct _cTemp
{
	unsigned int nSize;
	char *sData;
};

int main()
{
	_cTemp cTemp;
	cTemp.nSize = 0x41414141; // set uint to 'AAAA'

	cout << sizeof(_cTemp) << endl;

	cTemp.sData = new char [100];
	memset(cTemp.sData, 'A', 100); // set char array to A's

	cout << sizeof(_cTemp) + 100 << endl;

	cout.write((char *)&cTemp, sizeof(_cTemp) + 100);
	cout << endl;

	delete[] cTemp.sData;

	return 0;
}

the cout.write function always returns a bunch of random garbage when its meant to return 'AAAAAA....', also im not 100% sure if the size im using is right.

i know the sizeof(_cTemp) = 8 (uint+pointer), when i assign the pointer 100 chars, would the size be 108? (im assuming that the size of the pointer doesnt change?).

anyway, why isnt it displaying 'AAAA..'? it shows the first 4 A's for the uint but not for the char array.

I'm not really familiar with the way you would set everything to AAA. But I would do it like this.

Code:

for(int i=0;i<99;i++)
      cTemp.sData[i] = 'A';
cTemp.sData[100] = '\0'; //terminate char array

/

oh i always thought that the pointer and the data being pointed to was always sequential..

thanks for pointing that out, saved me quite a bit of trouble

actually, what im trying to do is convert a struct into a char array so i can send send() it using winsock.

it works fine when i use char sData[100], but if i use a pointer, the memory isnt sequential so its not working as i expected.

oh and btw:

Code:

for(int i=0;i<99;i++)
      cTemp.sData[i] = 'A';
cTemp.sData[100] = '\0'; //terminate char array

is wrong, it should be

Code:

// the array is 0-99 not 0-100
for(int i=0;i<99;i++)
      cTemp.sData[i] = 'A';
cTemp.sData[99] = '\0'; //terminate char array

i wasnt sure if the sent messages were recv'ed in sequential order, so i tried to limit every send to 1 packet. took me a few hours to get everything working, but its all good now.

Originally Posted by X PaYnE X

i wasnt sure if the sent messages were recv'ed in sequential order, so i tried to limit every send to 1 packet. took me a few hours to get everything working, but its all good now.

tcp will make sure your data arives in the same order that it was sent but you shouldn't depend on it being all recv()ed in one call.

thats strange, in a different client/server program i had, i sent 2 packets and it was received in the wrong order and since then i basically assumed i had to handle the sequencing manually.

not sure what could have caused it, probably the same thread accessing a global var at the same time.

another question if possible, is there a maximum limit on send/recv? (im currently limiting it to 1kb)