strtok_s 函数破坏程序

Question

I already read most of the answered questions about this function but I would like to now why is my code printing the tokens and yet breaking. I should use this function to extract the tokens from a string that has only the ' ' separator and to do some operations on them, but I tried first to just print the tokens, and if this would have worked perfectly, after to modify the tokens. This is not happening ... I wrote the code guided by the Help Viewer in Visual Studio 2015:

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

using namespace std;

int main()

{   char s[50] = "testing the strtok_s function", *token = NULL, *next_token = NULL;

    // Establish string and get the first token:

    token = strtok_s(s, " ", &next_token);
    cout << token << '\n';

    // While there are tokens in s:

    while (token != NULL)
    {   //Get the next token:

        if (token != NULL)
        {   token = strtok_s(NULL, " ", &next_token);
            cout << token << '\n';;
        }
    }
}

I get this result in the console, which makes me happy:

But, I also get this error, and a window called iosfwd pops and a arrow points on a line that probably explains the breaking reason: return (*_First == 0 ? 0

This is the error window:

Answer 1

You use token as input parameter of cout after the return of strtok_s , without testing whether it is null or not.

This is not safe and is probably the reason of your crash.

Try the following instead:

while (token != NULL)
{
    cout << token << '\n';
    token = strtok_s(NULL, " ", &next_token);
}

By doing so, you could remove the first call to cout .

Answer 2

Regarding the following two lines in your code:

token = strtok_s(NULL, " ", &next_token);
cout << token << '\n';;

Can you try explaining to your rubber duck what happens here when strtok_s () returns NULL to indicate that there are no more tokens to retrieve from your string?