Boost::format string examples
Once boost::format object has been created with a format string and given arguments, there are two ways of getting a std::string (or std::wstring) from it. One is with boost::str() and the other way is with str() member method.
Read also: Boost::format dates, time, horizontal alignment
Std::string
To begin with, we need to include the format library header. Create a format object. This is done by giving boost::format a string as the first argument.
#include <boost/format.hpp>
// Create a boost::format object,
boost::format formatobject("Pi is %4.2f");
Feed the format object with a value. Boost::format will remember the value and format it later:
// Feed it with Pi formatobject % 3.14;
At this point the format object has enough information to create a string for us. Just call either of boost::str() or formatobject.str().
// Get strings std::string str1 = boost::str(formatobject); std::string str2 = formatobject.str();
Now you can use str1 and str2 as a regular string with the value Pi is 3.14.
Read also: Boost::format numbers (int, float, double)
C-string
From here on it is easy to create a c-string. Remember the pointer is only valid as long as str1 is valid.
// Character array from the first string const char * char1 = str1.c_str();
Read also: 5 Great things about Boost
Const std::string
It is also possible to exploit a lesser known feature of C++, specially when dealing with large strings. To avoid the cost of copying the string, it is perfectly legal to use a const reference. This is also known as The most important const. Details can be found here: http://herbsutter.com/2008/01/01/gotw-88-a-candidate-for-the-most-important-const/.
const std::string & str3 = boost::str(formatobject); const std::string & str4 = formatobject.str();
The full example is available on Github.
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