Split string into substrings

[Manfr3d]

Hello guys, I want to split a string into substrings using strtok(). The code is

#include "stdafx.h"

#using #include #include #include using namespace System;
using namespace std;

char str2list(char* str, char** list, const char* delimiters)
{
for (char c = 0; c < sizeof(list) / sizeof(char*); c++)
{
list[c] = strtok(str, delimiters);
if (list[c] == NULL) break;
}
return c;
}

int _tmain()
{
char** arglist;
arglist = new char*[16];
char* exmp = "I have a problem!";
str2list(exmp, arglist, " ");
for (char c = 0; c < sizeof(arglist) / sizeof(char*); c++)
{
cout << arglist[c] << endl;
}
delete[] arglist;
return 0;
}

When I try to execute the program a runtime error occurs saying that there is a null-reference exception in the line list[c] = strtok(str, delimiters);. To ensure that there is enough free memory I even used the new operator. Does anyone have an idea why this doesn't work? Thanks and best wishes.

[Stuart Dootson]

Austrian_Programmer wrote:

When I try to execute the program a runtime error occurs saying that there is a null-reference exception in the line list[c] = strtok(str, delimiters);. To ensure that there is enough free memory I even used the new operator.

That's because (although exmp is a char*), it's pointing at a string stored in read-only memory (string literals are read-only). strtok needs to write to it. It can't, so you get a runtime exception. Change

char\* exmp = "I have a problem!";

to

char exmp\[\] = "I have a problem!";

and the crash goes away, because now you've allocated a read/write character array and initialised it from the (read-only) string literal. There are many other issues as well, however:

1. Look at the strtok documentation[^] - you only pass in str on the first call to strtok for that string - the rest of the time, you pass in NULL.
2. The loop condition in str2list is all wrong. list is a char**, so sizeof(list)/sizeof(char*) will be equal to 1. If you want to be safe with respect to the size of list, you need to explicitly pass it in - C/C++ doesn't pass around array sizes with arrays.
3. Similarly, the loop condition in _tmain is wrong (although this problem goes away if you take note of the next point).
4. There's no point using new when you have a fixed array size - declaring arglist with char* arglist[16]; will work just as well.
5. I'm...interested that you use char as the type of the loop variables
6. Although the for loop in str2list may compile with the compiler you're using, it won't with VS2008 (and possibly won't with earlier compilers), and isn't compliant with the C++ standard - going by the standard, your loop variable isn't accessible outside the loop.
7. You return the number of tokens in the list from str2list...and then don't use it. Mmmmm.

Anyway - here's my fixed (I think) version of your code.

#include <iostream>
#include <string.h>

using namespace std;

int str2list

[Manfr3d]

Thanks for the answer. I've done a lot of microprocessor programming in the last time and there I use char whenever possible (it's the smallest type and working without causing any troubles). However, that's pure C and there are (I know) a few differences to C++. Normally I use C++ for game programming and mathematical things and that's more or less the first time I do something with strings in C++, so this is all in all just a try.

[Stuart Dootson]

Austrian_Programmer wrote:

Normally I use C++ for game programming and mathematical things and that's more or less the first time I do something with strings in C++, so this is all in all just a try.

That's cool - if you're starting out with C++ on a desktop platform, I really would recommend learning about the Standard Template Library - it makes (some) things a lot easier, especially managing strings and arrays (or vectors, which is the closest thing to an array in STL)..

Java, Basic, who cares - it's all a bunch of tree-hugging hippy cr*p