Why strtok() don't work with char *?

[Ali Uruji]

Hi, I'm trying to write a simple program in VC++ 2010 to tokenize a sentence.
Yet, the code I wrote do not cause any compilation errors( regardless of warnings about strtok ) but when its executed it stops working. This is the code:

#include <iostream>
#include <cstring>

using namespace std;

int main(){
	char *line = "int a = 10, b; ";
	char *token;

	token = strtok( line, " " ); 

	cout << token;

        return 0;
}

This program seems to have a problem with strtok() because of these:



And one another thing: why when I change

 char *line

to

 char line[]

... it works correctly?

[horace1]

in line 7

    char *line = "int a = 10, b; ";

the text "int a = 10, b; " is a string constant and the gcc compiler displays the warning (if warnings are enbled)

 warning: deprecated conversion from string constant to 'char*'

therefore the variable line points to a string constant
you can print its contents OK so

   cout << line << endl;

because the statement does not attempt to modify the string

however, the first parameter to strtok() cannot be a pointer to a constant as the contents of the string are modified and broken into smaller strings (tokens) by strtok(). see

http://www.cplusplus.com/reference/clibrary/cstring/strtok/

it is when strtok() trys to modify the constant string "int a = 10, b; " the program crashes with a memory error.

changing line 7 to

    char line[] = "int a = 10, b; ";

works because the string not a constant it is an array which can be modified

[Banfa]

works because the string not a constant it is an array which can be modified

Strictly and pedantically speaking the string is still a constant but it is copied into a non-constant array of char line and this is what is modified.