Returning and Printing Strings in C++

Question

I am trying to get a file path from the user in the getPath() function and return the path as a string. I am having trouble because the compiler says i need to use const char's and i dont know how to do that. How would I use const chars and what even are they. Also how do I print them to the console like in the main function.

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

  char getPath() {
     char path[64];
     std::cout << "Input File Name For Debugging:";
     gets(path);
     std::cout << "Debugging: ";
     puts(path);
     return path[64];
 }

int main(){
    char path[64];
    int pathlen = strlen(reinterpret_cast<const char *>(path));
    //suppost to print the char array
    for(int i; i < pathlen; i++){
        std::cout << path[i];
    }
     return 0;
 }

Aside: `getPath` is not designed properly and neither it is called. Many things are uninitialized in your code. — Ardent Coder, Apr 08 '20 at 04:40
Where are you learning all of this? Your code is C with `std::cout`, not C++. Also, `gets` is evil. It's deprecated in C++11 and removed in C++14. You're being taught "C with classes" which is not proper C++. — eesiraed, Apr 08 '20 at 04:40
I know that these function are unprotected and can be overflowed easily. I am using it to learn binary exploitation. I got most of this from cplusplus.com, if there is a better site please let me know. — Harrison Brammell, Apr 08 '20 at 04:43
I don't mean to offend you but you should really master programming before trying to learn binary exploitation. You know the problems with `gets` so don't use it unless you're trying to write a vulnerable program. Learning basic C++ from websites usually don't end well, so you should get a [good book](https://stackoverflow.com/q/388242/9254539) instead. — eesiraed, Apr 08 '20 at 04:47

john · Answer 1 · 2020-04-08T05:31:22.003

Lot's of misunderstandings

1) char is not a string, it's a character

2) An array of chars (e.g. char [64]) is not a string, its an array. It can hold a string but that's a subtly different idea

3) You don't use [64] when you mean the whole array, so return path[64]; is not the correct way to return a string.

4) Don't mix C++ I/O (std::cin, std::cout) with C I/O (puts, gets), it doesn't work reliably, Stick with C++ I/O so

 std::cout << "Debugging: " << path << '\n';

not

 std::cout << "Debugging: ";
 puts(path);

5) You never call your getPath function so of course it doesn't execute

6) You don't initialise your loop variable i in your final loop so it has no predictable value. You should initialise i to 0

for(int i; i < pathlen; i++){
     std::cout << path[i];

should be

for(int i = 0; i < pathlen; i++){
     std::cout << path[i];

As you can see lots and lots of mistakes for a very short program. I'm going to show two different correct ways to write this program.

So there are two ways to represent a string in C++, there's the C++ way and there's the way that C++ inherits from C. The code you are writing above is trying to do things the C way, so I'll show that first, but actually the C++ way is much much easier. I'll show that second, but it's the way you should do things.

The first way is to use an array of characters to hold the string. But arrays have serious problems in C++. In particular it's not possible to return an array from a function, so your code above was never going to work, even if you'd fixed all the smaller problems. The way you get C++ to 'return' an array is a bit curious and I'm not going to explain it properly (you need to read a good C++ book). What you do is declare the array in the calling function and pass the array as a parameter. Here's your program written using this technique (and fixed of all the other problems).

#include <iostream>

void getPath(char path[], int n) {
     std::cout << "Input File Name For Debugging:";
     std::cin.getline(path, n);
     std::cout << "Debugging: " << path << '\n';
}

int main(){
    char path[64];
    getPath(path, 64);
    std::cout << path << '\n';
    return 0;
}

Note I'm using getline to read the string, which is one C++ way to read a string. getline requires that you pass the size of the array it's going to read into, so I've passed that to getPath as well as the array itself.

Now for the easy way. C++ has it's own string type called std::string. You don't need to use tricky arrays at all. And the C++ string type can be returned from a function in the normal way. This makes for much more natural code. To use the C++ string type all you need to do is #include <string>. Here's your program rewritten to use the C++ string type

#include <iostream>
#include <string>

std::string getPath() {
     std::cout << "Input File Name For Debugging:";
     std::string path;
     std::getline(std::cin, path);
     std::cout << "Debugging: " << path << '\n';
     return path;
}

int main(){
    std::string path;
    path = getPath();
    std::cout << path << '\n';
    return 0;
}

Notice this second program is closer to your original code, getPath has a return type, only it's std::string not char, and it has a return statement to return the path. This is the way you should be writing this code, the C++ string type will make writing string code much easier for you.

Returning and Printing Strings in C++

1 Answers1