tsf - A type safe printf-compatible C++ library

Type safe
Small (less than 700 lines)
Use as either two files (tsf.cpp and tsf.h, or header-only tsf.hpp)
Compatible with printf formatting rules
Optional interface to provide own buffer

Example

tsf::fmt("%v %v", "abc", 123);        // -->  "abc 123"     <== Use %v as a generic value type
tsf::fmt("%s %d", "abc", 123);        // -->  "abc 123"     <== Auto fixup if your type is wrong
tsf::fmt("%v", std::string("abc"));   // -->  "abc"         <== std::string
tsf::fmt("%v", std::wstring("abc"));  // -->  "abc"         <== std::wstring
tsf::fmt("%.3f", 25.5);               // -->  "25.500"      <== Use format strings as usual
tsf::print("%v", "Hello world");      // -->  "Hello world" <== Print to stdout
tsf::print(stderr, "err %v", 5);      // -->  "err 5"       <== Print to stderr (or any other FILE*)
tsf::fmt_buf(buf, bufLen, "%v", 5);   // Writes to user-provided buffer. See header for more.

Implementation

tsf uses snprintf as a backend, so all of the regular formatting commands that you expect from the printf family of functions work. This makes the code much smaller than other implementations.

To improve speed, some common operations are implemented locally (e.g. emitting integers or plain strings). Most snprintf implementations are actually quite slow, and we can gain a lot of speed by doing these common operations ourselves.

Known unsupported features

Positional arguments
%*s (integer width parameter) -- wouldn't be hard to add. Presently ignored.

Usage

If you specify invalid formatting types (eg %f instead of %d), then tsf rewrites your formatting symbol with one that is compatible with the actual type passed in. For example, if you say %d, and you pass in a const char*, then the %d is rewritten into %s.

Generally, you just use %v, which stands for "value".

tsf is very light on templates - it uses them only for type safe variadic argument lists, so impact on compile times is negligible.

To use tsf, choose one of:

Add tsf.cpp to your project, and #include "tsf.h".
#include "tsf.hpp" wherever you need it.

API

fmt           returns std::string.
fmt_buf       is useful if you want to provide your own buffer to avoid memory allocations.
print         prints to stdout
print(FILE*)  prints to any FILE*

By providing a cast operator to fmtarg, you can get an arbitrary type supported as an argument, provided it fits into one of the molds of the printf family of arguments.

tsf also support two custom types: %Q and %q. In order to use these, you need to provide your own implementation that wraps one of the lower level fmt_core functions, and provides a context object with custom functions defined for Escape_Q and Escape_q. These were originally added in order to provide quoting and escaping for SQL identifiers and SQL string literals.

Test

clang -O2 test.cpp tsf.cpp -std=c++11 -lstdc++ -lm && ./a.out
gcc -O2 test.cpp tsf.cpp -std=c++11 -lstdc++ -lm && ./a.out