C++ how to use a variable in a string

Question

The following code doesn't work:

string currency;
currency = "EURUSD";

system("lynx -dump 'http://somesite.com/q?s="+currency+"=X' > file.txt");

How do I use currency inside this line of C++'s system() call?

This is my error:

Error value:
main.cpp: In function ‘int main()’:
main.cpp:22:84: error: cannot convert ‘std::basic_string<char>’ to ‘const char*’ for argument ‘1’ to ‘int system(const char*)’
make: *** [main.o] Error 1
BUILD FAILED (exit value 2, total time: 890ms)

In PHP I use . to join strings, but in C++ I am not sure of the syntax.

Answer 1

Using stringstream:

#include <sstream>
string currency;
currency = "EURUSD";
std::stringstream ss;
ss << "lynx -dump 'http://somesite.com/q?s=" << currency << "=X' > file.txt";
system(ss.str().c_str());

Answer 2

std::string::c_str() will give you a char* (const'd somehow) that you can use in C string functions. But you should consider creating a std::string that contains the full command first.