modernize-use-std-format

Converts calls to absl::StrFormat, or other functions via configuration options, to C++20’s std::format, or another function via a configuration option, modifying the format string appropriately and removing now-unnecessary calls to std::string::c_str() and std::string::data().

For example, it turns lines like

return absl::StrFormat("The %s is %3d", description.c_str(), value);

into:

return std::format("The {} is {:3}", description, value);

The check uses the same format-string-conversion algorithm as modernize-use-std-print and its shortcomings are described in the documentation for that check.

Options

StrictMode

When true, the check will add casts when converting from variadic functions and printing signed or unsigned integer types (including fixed-width integer types from <cstdint>, ptrdiff_t, size_t and ssize_t) as the opposite signedness to ensure that the output would matches that of a simple wrapper for std::sprintf that accepted a C-style variable argument list. For example, with StrictMode enabled,

extern std::string strprintf(const char *format, ...);
int i = -42;
unsigned int u = 0xffffffff;
return strprintf("%d %u\n", i, u);

would be converted to

return std::format("{} {}\n", static_cast<unsigned int>(i), static_cast<int>(u));

to ensure that the output will continue to be the unsigned representation of -42 and the signed representation of 0xffffffff (often 4294967254 and -1 respectively). When false (which is the default), these casts will not be added which may cause a change in the output. Note that this option makes no difference for the default value of StrFormatLikeFunctions since absl::StrFormat takes a function parameter pack and is not a variadic function.

StrFormatLikeFunctions

A semicolon-separated list of (fully qualified) function names to replace, with the requirement that the first parameter contains the printf-style format string and the arguments to be formatted follow immediately afterwards. The default value for this option is absl::StrFormat.

ReplacementFormatFunction

The function that will be used to replace the function set by the StrFormatLikeFunctions option rather than the default std::format. It is expected that the function provides an interface that is compatible with std::format. A suitable candidate would be fmt::format.

FormatHeader

The header that must be included for the declaration of ReplacementFormatFunction so that a #include directive can be added if required. If ReplacementFormatFunction is std::format then this option will default to <format>, otherwise this option will default to nothing and no #include directive will be added.