strcpy compiles on Windows but it doesn't on Linux

Question

I'm learning C++ and trying to write universal code (sorry, I don't know how you call the code that can compiles on Windows, Linux, MacOS, etc.).

I have written the function trimLeft:

#include <iostream>
#include <fstream>
#include <string>

using namespace std;

const string rows = "rows:";
const string columns = "cols:";
const string data = "data:";

struct dimensions {
    int rows;
    int columns;
};

inline bool exists (const string& name) {
    ifstream f(name.c_str());
    return f.good();
}

string trimLeft(const string& input) {

    if ((input.empty()) || 
        ((input.at(0) != ' ') && (input.at(0) != '\t')))
        return input;
    else {
        char * tab2 = new char[input.length() + 1];
        char *trimmed = new char[input.length() + 1];

        strcpy(tab2, input.c_str());

        bool skip = true;
        int pos = 0;

        for (unsigned int i = 0; i < (input.length() + 1); i++) {
            if (skip) {
                if ((tab2[i] == ' ') || (tab2[i] == '\t'))
                    continue;
                else {
                    skip = false;

                    trimmed[pos] = tab2[i];
                    pos++;
                }
            }
            else {
                trimmed[pos] = tab2[i];

                if (tab2[i] == '\0')
                    break;
                else
                    pos++;
            }
        }

        string stringTrimmed(trimmed);

        return stringTrimmed;
    }
}

It compiles on Windows showing this warning:

warning C4996: 'strcpy': This function or variable may be unsafe. Consider using strcpy_s instead. To disable deprecation, use _CRT_SECURE_NO_WARNINGS.

But in Linux, with the following command:

g++ FormatMatrix.cpp -o format

I get:

error: ‘strcpy’ was not declared in this scope

Are headers different on each operating system?

NOTE:
And please, stop voting negative: I've got the message.

`#include ` . Though it's unclear why you want to use raw `char` arrays to begin with, when you know how to use `std::string`. — Igor Tandetnik, Jun 21 '19 at 15:23
Include the [`cstring` header](https://en.cppreference.com/w/cpp/string/byte/strcpy) to make your code portable. — πάντα ῥεῖ, Jun 21 '19 at 15:24
@VansFannel _"Do I have to include instead of ?"_ For sake of portability, yes. — πάντα ῥεῖ, Jun 21 '19 at 15:25
``: `std::string` and friends, ``: provides C API for string things (`string.h`) — Scheff's Cat, Jun 21 '19 at 15:26
Why do you use cstrings? You have memory leaks in your code. You allocate memory but you don't free it. — Thomas Sablik, Jun 21 '19 at 15:26
You are doing `new` without `delete`, you definitely have a memory leak. — , Jun 21 '19 at 15:28
Avoid cstrings. Avoid raw pointers. Avoid memory allocation. Use stl containers. You are currently learning bad coding style. — Thomas Sablik, Jun 21 '19 at 15:29
and `using namespace std` is also a habit you should not acquire. Don't do that. — , Jun 21 '19 at 15:31
@VansFannel _"(sorry, I don't know how you call the code that can compiles on Windows, Linux, MacOS, etc.)"_ It's called _portable code_. — πάντα ῥεῖ, Jun 21 '19 at 15:33
-4 to ask about something I don’t know (to try lesrn something new). I don’t understand StackOverflow. — VansFannel, Jun 22 '19 at 06:57
@VansFannel The negative votes are probably from a combination of you trying to learn a bad idea _(resorting to C-style strings when you started with `std::string` -- see also [Trim white space from string](https://codereview.stackexchange.com/a/40302))_ and of your code being much longer than necessary to present your problem _(see [mcve])_. — JaMiT, Jun 23 '19 at 22:28
@VansFannel If you got your question down to just what you need to reproduce the error message on Windows, you'd probably have a duplicate of [C++ 'strcpy' gives a Warning (C4996)](https://stackoverflow.com/questions/4012222/c-strcpy-gives-a-warning-c4996). — JaMiT, Jun 23 '19 at 22:36

score 1 · Accepted Answer · answered Jun 21 '19 at 15:28

It is entirely possible that as an implementation detail for a particular compiler, <cstring>, which includes the declaration of strcpy, is included (perhaps much further up the inclusion tree) by another header you included.

To ensure that your code is truly portable and standard conforming include the header files for every class and function you call; never take for granted that you get the functionality of another header by including something different.

strcpy compiles on Windows but it doesn't on Linux

1 Answers1