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C++ Format v0.10.0 Release Notes

Release Date: 2014-07-01 // almost 10 years ago

  • 👌 Improved API

    • All formatting methods are now implemented as variadic functions instead of using operator<< for feeding arbitrary arguments into a temporary formatter object. This works both with C++11 where variadic templates are used and with older standards where variadic functions are emulated by providing lightweight wrapper functions defined with the FMT_VARIADIC macro. You can use this macro for defining your own portable variadic functions:

    .. code:: c++

    void report_error(const char *format, const fmt::ArgList &args) {
  fmt::print("Error: {}");
  fmt::print(format, args);
}
FMT_VARIADIC(void, report_error, const char *)

report_error("file not found: {}", path);

    Apart from a more natural syntax, this also improves performance as there is no need to construct temporary formatter objects and control arguments' lifetimes. Because the wrapper functions are very lightweight, this doesn't cause code bloat even in pre-C++11 mode.

    • Simplified common case of formatting an std::string. Now it requires a single function call:

    .. code:: c++

    std::string s = format("The answer is {}.", 42);

    Previously it required 2 function calls:

    .. code:: c++

    std::string s = str(Format("The answer is {}.") << 42);

    Instead of unsafe c_str function, fmt::Writer should be used directly to bypass creation of std::string:

    .. code:: c++

    fmt::Writer w;
w.write("The answer is {}.", 42);
w.c_str();  // returns a C string

    This doesn't do dynamic memory allocation for small strings and is less error prone as the lifetime of the string is the same as for std::string::c_str which is well understood (hopefully).

    • 👌 Improved consistency in naming functions that are a part of the public API. Now all public functions are lowercase following the standard library conventions. Previously it was a combination of lowercase and CapitalizedWords. Issue #50 <https://github.com/fmtlib/fmt/issues/50>_.

    • 🚚 Old functions are marked as deprecated and will be removed in the next release.

    Other Changes

    • 🚧 Experimental support for printf format specifications (work in progress):

    .. code:: c++

    fmt::printf("The answer is %d.", 42);
std::string s = fmt::sprintf("Look, a %s!", "string");
    • 👌 Support for hexadecimal floating point format specifiers a and A:

    .. code:: c++

    print("{:a}", -42.0); // Prints -0x1.5p+5
print("{:A}", -42.0); // Prints -0X1.5P+5
    • 🏗 CMake option FMT_SHARED that specifies whether to build format as a shared library (off by default).