Programming Forums > Application Development > C++

DaWei · Mar 29th, 2006, 9:00 AM

In C/C++, arrays (including 'C-strings', arrays of char) are not atomic objects that can be assigned or compared with the =, ==, >=, etc., operators.

The statement, "if (myString == "abcd"), will, in fact, compare the two pointers, NOT the contents referenced by those pointers.

Just thought you'd like to know, in case you don't read (or comprehend) the multidinous threads on the forum that impart this fact.

zorin · Mar 29th, 2006, 9:30 AM

Phew...for a minuite there I thought you were asking for help

DaWei · Mar 29th, 2006, 12:18 PM

Hey, I ask for help when I can't find the answer by searching! (Admittedly, I search other forums as well as this one, I just don't recommend that out loud to the members here.)

MBirchmeier · Mar 29th, 2006, 12:48 PM

What's the context for this spontanious outburst? Has this been plagueing your thoughts recently? Or have questions like these been plagueing this (or other) forums?

-MBirchmeier

nnxion · Mar 29th, 2006, 12:52 PM

Quote:

Originally Posted by DaWei

Hey, I ask for help when I can't find the answer by searching! (Admittedly, I search other forums as well as this one, I just don't recommend that out loud to the members here.)

I don't ask or search other forums, if I don't understand it (right away), and people here can't explain it to me, the chances are very high that at the other forums they can't explain it either (Unless my problem applies to MS specific compiler settings or the like, in which case I would go to the MS forums).

Cipher · Mar 29th, 2006, 1:49 PM

So this means you can't do something like this?:

(Toggle Plain Text)

string message[1];
if (message[1] == "whatever")
etc.

That won't work?

jayme · Mar 29th, 2006, 2:11 PM

Quote:

Originally Posted by Cipher

So this means you can't do something like this?:

(Toggle Plain Text)

string message[1];
if (message[1] == "whatever")
etc.

That won't work?

Yes, that does work.

nnxion · Mar 29th, 2006, 2:12 PM

Quote:

Originally Posted by Cipher

So this means you can't do something like this?:

(Toggle Plain Text)

string message[1];
if (message[1] == "whatever")
etc.

That won't work?

Exactly. "whatever" is still a char array (C string), and thus a comparing a pointer to an object of type string, can not be done, will result in a compiler error complaining not being able to match arguments std::string, and a const char.

Edit:

Quote:

Originally Posted by jayme

Yes, that does work.

Yes it does work, but only because the string class provides the == operator.

(Toggle Plain Text)

#include <iostream>
#include <string>

using namespace std;

int main()
{
	string message[1];
	message[0] = "hello";

	if (message[0]   == "hello")
		cout << "hello" << endl;
	else
		cout << "bye" << endl;
	return 0;
}

Seif · Mar 29th, 2006, 2:15 PM

nope, use the string compare function.

(Toggle Plain Text)

string message[1];

if (strcmp(message[0], "whatever") ==  0)

etc

Must admit I understand where Dawai is coming from, have seen a couple of posts recently where there seems to be confusion with pointers and arrays. Was going to refer them to Dawai's tutorial on pointers as I'm not too up to scratch on them myself.

Seif · Mar 29th, 2006, 2:17 PM

bah missed those last 2 posts by jayme and nnxion sorry.

Mar 29th, 2006, 9:00 AM	#1
DaWei Resident Grouch Join Date: Jun 2005 Posts: 6,453 Rep Power: 10	Arrays In C/C++, arrays (including 'C-strings', arrays of char) are not atomic objects that can be assigned or compared with the =, ==, >=, etc., operators. The statement, "if (myString == "abcd"), will, in fact, compare the two pointers, NOT the contents referenced by those pointers. Just thought you'd like to know, in case you don't read (or comprehend) the multidinous threads on the forum that impart this fact. __________________ Abstraction doesn't make it impossible to write bad code; it makes it possible to write superior code. Contributor's Corner: Grumpy on C++ Exceptions DaWei on Pointers

Mar 29th, 2006, 12:18 PM	#3
DaWei Resident Grouch Join Date: Jun 2005 Posts: 6,453 Rep Power: 10	Hey, I ask for help when I can't find the answer by searching! (Admittedly, I search other forums as well as this one, I just don't recommend that out loud to the members here.) __________________ Abstraction doesn't make it impossible to write bad code; it makes it possible to write superior code. Contributor's Corner: Grumpy on C++ Exceptions DaWei on Pointers

Mar 29th, 2006, 1:49 PM	#6
Cipher Hobbyist Programmer Join Date: Feb 2005 Location: /home/cipher Posts: 123 Rep Power: 4	So this means you can't do something like this?: (Toggle Plain Text) string message[1]; if (message[1] == "whatever") etc. string message[1]; if (message[1] == "whatever") etc. That won't work? __________________ And there was much rejoicing... Yay....

Mar 29th, 2006, 2:15 PM	#9
Seif Hobbyist Programmer Join Date: Jan 2006 Location: UK Posts: 215 Rep Power: 3	nope, use the string compare function. (Toggle Plain Text) string message[1]; if (strcmp(message[0], "whatever") == 0) etc string message[1]; if (strcmp(message[0], "whatever") == 0) etc Must admit I understand where Dawai is coming from, have seen a couple of posts recently where there seems to be confusion with pointers and arrays. Was going to refer them to Dawai's tutorial on pointers as I'm not too up to scratch on them myself.

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Mar 29th, 2006, 9:30 AM	#2
zorin Hobbyist Programmer Join Date: Apr 2005 Posts: 218 Rep Power: 4	Phew...for a minuite there I thought you were asking for help

Mar 29th, 2006, 12:48 PM	#4
MBirchmeier Hobbyist Programmer Join Date: Oct 2005 Posts: 211 Rep Power: 3	What's the context for this spontanious outburst? Has this been plagueing your thoughts recently? Or have questions like these been plagueing this (or other) forums? -MBirchmeier

Mar 29th, 2006, 2:17 PM	#10
Seif Hobbyist Programmer Join Date: Jan 2006 Location: UK Posts: 215 Rep Power: 3	bah missed those last 2 posts by jayme and nnxion sorry.

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Programming Forums > Application Development > C++

Arrays