How to concate two pointer character? - c++

Question

I am building a fast copy application using xcopy. I want to pass two variable source and destination to system(); I am trying like this
char *source = "D:\\SOFTWARE\\Internet";
char *destination = " D:\\test /s /e /d /y";
system("xcopy "+source+destination);
But it doesnt work. It work fine in java. same code. Thanks.

Answer 1

Rewriting Mike's code to eliminate all the issues we tend to flag in code being reviewed!
#include <string>
#include <cstdlib>
using std::string;
int main()
{
const string str{ "dir" };
const string str2{ " /w" };
const string final_string = str + str2;
std::system(final_string.c_str());
}
Your problem in your original code is that operator+ doesn't work with C style strings, which are just char* or char[] and not objects. You are asking to add pointers together, which is not a sensible thing.
As Mike points out, turn your raw char array input into std::string objects as soon as you need to do stuff with it, and then + will work.
In this particular case, you only need to copy one of the character arrays into objects (see docs on operator+= form 3):
string s {"xcopy "};
s += source;
s += destination; // this works, as there is an optimized form of operator+ for this.
std::system(s.c_str()); // access a nul-terminated character array to make the system call.

Answer 2

One more way of string concatenation is use of std::ostringstream. Source and destination paths are quoted in the code bellow to be more safe:
#include <sstream>
int main() {
const char *source = "\"D:\\SOFTWARE\\Internet\"";
const char *destination = " \"D:\\test\" /s /e /d /y";
std::ostringstream cmd;
cmd << "xcopy " << source << destination;
system(cmd.str().c_str());
}
Compile and run

Answer 3

You need to use std::string (from string header). Also, you need to go from string to a const char pointer.
#define _CRT_SECURE_NO_DEPRECATE
#include <cstdlib>
#include <string>
int main()
{
using namespace std;
string str{ "dir" };
string str2{ " /w" };
string final_string = str + str2;
char* cstr = new char[final_string.size() + 1];
strcpy(cstr, final_string.c_str());
system(cstr);
}