How to build a full path string (safely) from separate strings?

Only as part of Boost.Filesystem library. Here is an example:

#include <iostream>
#include <boost/filesystem.hpp>

namespace fs = boost::filesystem;

int main ()
{
    fs::path dir ("/tmp");
    fs::path file ("foo.txt");
    fs::path full_path = dir / file;
    std::cout << full_path << std::endl;
    return 0;
}

Here is an example of compiling and running (platform specific):

$ g++ ./test.cpp -o test -lboost_filesystem -lboost_system
$ ./test 
/tmp/foo.txt