How to fix the compiler error: "'strtok' function may be unsafe"

Question

I'm currently writing a program that can convert several mathematical functions, like converting floats to cosines, natural logs, etc. I'm also include a way to convert a date format of m/dd/yyyy, to the format of mm-dd-yyyy. I'm trying to token c-string by the '/' and then concatenate it back together with '-'. The problem is visual studio's gives me a C4996 error code, and says my function may be unsafe. I'm aware I can turn this off so they don't give me these kinds of warnings, but when I run the program, the strtok function doesnt appear to do anything.

#include <iostream>
#include <cstring>
using namespace std;

//KEEP IN MIND THIS IS ONLY ONE PART OF THE PROGRAM, I have more includes, and this is under the main function. (I only included relevant includes)

//If they enter 4 to convert a cstring date.
    if (input == 4) {
        cout << "You entered: change the format of a cstring date" << endl;
        cout << "Please enter a date in the format of mm/dd/yyyy: " << endl;
        char str[12];   //C-String to hold input
        cin >> str;
        //Create an char[] to hold the answer
        char newStr[32];
        // Returns first token  
        char* token = strtok(str, "/");
        // Keep printing tokens while one of the 
        // delimiters present in str[]. 
        while (token != NULL)
        {
            strcat_s(newStr, token);    //Cat it to string
            strcat_s(newStr, "-");  //Add the -
            token = strtok(NULL, "/");
        }

        cout << "Your new Date is: " << newStr;
        return 0;
    }

Even when I bypass the error message, and run the program, enter for example: 11/22/3333 I recieve an output of 11/22/3333

At least you need to store an empty string in the array newStr. char newStr[32]; newStr[0] = '\0'; Or char newStr[32] = ""; .Or char newStr[32] = {}; Otherwise a call of strcat_s will result in undefined behaviour. — Vlad from Moscow, Jun 01 '19 at 13:25
Okay thanks, I fixed that issue in my code, but I still receive a problem with the strtok function. Is it a similar issue to making it an empty string? — leifoftrees, Jun 01 '19 at 13:30
Is there a reason why not simply replace '/' with '-' in a loop over `str`? — Quimby, Jun 01 '19 at 13:32
@leifoftrees Insert a test printing of the pointer token within the loop. For example std::cout << token << '\n'; — Vlad from Moscow, Jun 01 '19 at 13:37
Why are you using C strings at all? `char str[12]; cin >> str;` is a buffer overflow waiting to happen. — melpomene, Jun 01 '19 at 13:37
@Quimbly , good idea, thank you I did it and it worked well. — leifoftrees, Jun 01 '19 at 13:49

How to fix the compiler error: "'strtok' function may be unsafe"

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