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.

Answer 1

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.