Why does std / boost::format cause this c_str() behaviour? - c++

Question

I'm using boost::format (not std:: as I'm using c++98) to format a string that I'm passing to a system() call.
When getting the c_str() of the string created by format, it seems to terminate halfway along the string. The same sting created with the literal value does not have the same problem. What's going on here?
Using Boost 1.46.1 according to BOOST_VERSION.
#include <boost/format.hpp>
#include <iostream>
#include <string>
int main(int argc, char** argv)
{
const std::string my_str = "echo '/%1%/ some other stuff'";
boost::format fmtr(my_str);
fmtr % "sleep 3"; // should read: echo '/sleep 3/ some other stuff'
std::cout << "1: " << fmtr.str() << "\n"; // 1. echo '/sleep 3/ some other stuff' (OK)
std::cout << "2: " << fmtr.str().c_str() << "\n"; // 2. echo '/sleep 3 (BAD)
// Try the c_str of a string not created through boost::format
const std::string finished = "echo '/sleep 3/ some other stuff'";
std::cout << "3: " << finished.c_str() << "\n"; // 3. echo '/sleep 3/ some other stuff' (OK)
// Try copying the string from format to see if that makes any difference (it doesn't)
std::string copy = fmtr.str();
std::cout << "4: " << copy.c_str() << "\n"; // 4. echo '/sleep 3 (BAD)
return 0;
}
Passing the c_str() to my system() call is resulting in the error:
sh -c: line 0: unexpected EOF while looking for matching `''
Presumably because it is finishing halfway along the string as well.

Answer 1

With proper includes your program works fine: ideone
#include <boost/format.hpp>
#include <iostream>
#include <string>
int main()
{
const std::string my_str = "echo '/%1%/ some other stuff'";
boost::format fmtr(my_str);
fmtr % "sleep 3"; // should read: echo '/sleep 3/ some other stuff'
std::cout << "1: " << fmtr.str() << "\n"; // 1. echo '/sleep 3/ some other stuff' (OK)
std::cout << "2: " << fmtr.str().c_str() << "\n"; // 2. echo '/sleep 3 (BAD)
// Try the c_str of a string not created through boost::format
const std::string finished = "echo '/sleep 3/ some other stuff'";
std::cout << "3: " << finished.c_str() << "\n"; // 3. echo '/sleep 3/ some other stuff' (OK)
// Try copying the string from format to see if that makes any difference (it doesn't)
std::string copy = fmtr.str();
std::cout << "4: " << copy.c_str() << "\n"; // 4. echo '/sleep 3 (BAD)
}
You should fix includes and return type of main and try again. If wrong behavior persist most probably you have broken version of c++ and/or boost library.