[Dev] null terms for strings

[Tanner Lovelace]

On Tue, 2002-05-07 at 14:30, M. Mueller wrote:
> Here's a little program that captures a problem I had today.  I have a map 
> container, map<string, t_myStruc), that I want to duplicate on another 
> machine.  I pack each entry into datagram and send it via sockets to another 
> machine where each packet is collected and used to build a copy of the map 
> entry by entry.  So, I convert the string key to an array of chars for the 
> journey to the other side.  In the process I got confused about the function 
> of null terminators on char array strings versus string objects.
> 

Well, for one thing, a C++ string may or may not be null terminated.
Officially, it's not specified as to how they are stored internally.
So, when in doubt, assume it's not.

> To compile: g++ -o test test.cpp
> 
> <snip start>
> #include <string>
> using namespace std;
> 
> main()
> {
> 	string a;
> 	a  = 'a';
> 	a += ' ';
> 	a += 's';
> 	a += 't';
> 	a += 'r';
> 	a += 'i';
> 	a += 'n';
> 	a += 'g';
> 	a += '\0';
> 	string b;
> 	b  = 'a';
> 	b += ' ';
> 	b += 's';
> 	b += 't';
> 	b += 'r';
> 	b += 'i';
> 	b += 'n';
> 	b += 'g';
> 
> 	if (a == b) 
> 		cout << "a equals b\n";
> 	else
> 		cout << "a not equals b\n";
> 
> 	if (strcmp(a.c_str(), b.c_str()) == 0)
> 		cout << "a.c_str() equals b.c_str()\n";
> 	else 
> 		cout << "a.c_str() not equals b.c_str()\n";
> 	
> }
> <snip end>


Well, I haven't run it, but just looking at it, I'd say the
strings are not the same.  String a has a null character at
the end and string b doesn't.  

In addition, I'd be interested in seeing what the .c_str() 
function returned.  I'd bet it doesn't do any checking for
stuff like this and the c-style strings that get returned
*are* the same (because they *must* have a null at the end)
even though the C++ strings are not.

I would just suggest sending over the output of the .c_str()
function of each string and then using the string constructor
to recreate them on the other side.

Tanner
-- 
Tanner Lovelace | lovelace@wayfarer.org | http://wtl.wayfarer.org/
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