This code accompanies the article "Type-Safe Formatting" in C/C++ Users Journal, July 2005. It implements a simple printf emulation framework, which is typesafe at the price of a slightly modified invocation syntax.
flex_string is a drop-in replacement for the standard string (std::basic_string, better known by its typedefed name, std::string. If you think that reimplementing a likely fine-tuned component of your standard library is not a very rewarding endeavor, think again. flex_string has a policy-based design allowing unparalleled control over its behavior and optimizations, and also allows you to define new implementations in only a few dozens of lines of code. If you're looking for controllable performance and predictible behavior with multiple threads, then flex_string might be of interest to you.
To find more about flex_string, you may want to read
"A Policy-Based basic_string Implementation,"
C/C++ Users Journal, June 2001.
The downloadable code consists of the flex_string header and a test suite that compares its behavior against std::string. Though no performance comparison suite is available at this time, Harmut Kaizer reported that simply dropping in flex_string in the Wave Boost Preprocessor improved its speed by 5-10%, depending on input.
Justin Matthews contributed with flex_string_hash.h, an add-on for flex_string that allows using it with hash maps. Justin's code supports (and automatically recognizes) two implementations: STLPort and Microsoft Visual C++ 7.1.