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Questions tagged [fmt]

The {fmt} formatting library and the C++ text formatting and output facility (C++20 `std::format` and C++23 `std::print`).

{fmt} is an open source formatting library for . It is similar in functionality to and sprintf. The formatting facility defined in the <format> header is based on it and provides a subset of {fmt}'s functionality.

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What's the simple way to print or format a custom type with libfmt?

Suppose I've defined some type, e.g. struct Foo { int a; float b; }; If I want to stream it to an ostream, I write an operator<< function, e.g.: std::ostream& operator<<(std::ostream& os, const Foo& foo) { return os << '(' << a << ',' << b <<…
einpoklum
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Custom formatting of the elements of std::vectors using the fmt library

While I can use to readily output the contents of a std::vector, I'm at a loss to format the display of its elements according to my preferences. #include #include int main() { double x1 =…
marital_weeping
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Generating compile time functions string for formatting strings with libfmt

I want to create a nice table in stdout. The table has a lot of headers that are mainly compiletime strings. For example: std::cout << fmt::format("|{0:-^80}|\n", "File Information"); The above prints: |-----------------------------File…
DEKKER
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fmt Library - Formatting to a (compile-time) string_view

I would like to use the fmt library to create a string_view from my format args. There is plenty documented about passing in a compile-time string as the format string, however, I want to output a compile-time string, so that I may use it in other…
stellarpower
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Technical background to the C++ fmt::print vs. fmt::format_to naming?

Why is it fmt::format_to(OutputIt, ...) and not fmt::print(OutputIt, ...)?? I'm currently familiarizing myself with {fmt}, a / the modern C++ formatting library. While browsing the API, I found the naming a bit disjoint, but given my little-to-no…
Martin Ba
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C++ {fmt} library, user-defined types with nested replacement fields?

I am trying to add {fmt} into my project, and all is going well, except I hit a little snag when trying to add a user-defined type for my simple Vec2 class. struct Vec2 { float x; float y; }; What I would like is to be able to use the same format…
BeigeAlert
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Overloading between printf functions and fmt functions

I have a class that takes a C printf set of variadic arguments in its constructor, like this: class Foo { public: Foo(const char* str, ...) __attribute__((format(printf, 2, 3))); Now I want to be able to use the fmt library with this class. If…
MadScientist
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How do I efficiently forward the formatting arguments when implementing a formatter for a custom type

I am trying to write a custom formatter to help me print vectors. I am attempting to maintain the format specifiers so that each item in the vector is formatted the same way. I have taken most of my inspiration from this tutorial, and the…
Troyseph
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Quote a string using {fmt}

Is there any way to print a string as quoted using {fmt}? Here is an example code showing what I want to achieve: fmt::print("Hello {}!", "Terens"); I want the code to print Hello "Terens"! instead of just Hello Terens!. EDIT: I want to use the API…
Terens Tare
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Cannot format argument from within spdlog

I am trying to use spdlog. I incorporated it with my code, but now I am getting the following error: ....fmt\core.h(1016): error C2338: Cannot format argument. To make type T formattable provide a formatter specialization:…
CygnusX1
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Linking errors with fmt: undefined reference to `std::string fmt::v6::internal::grouping_impl(fmt::v6::internal::locale_ref)'

In our project, we decided to use the latest fmt version(6.2.0) in our project and use mainly the printf functionality as we had our logging where we are using printf extensively. I built the libfmt.a on our Linux box using the CMakeLists.txt…
psingh
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Convention on printing STL containers for approval tests

I'm writing approval tests using the excellent ApprovalTests.cpp library. This library automates generation of "snapshots" of results from a function. Snapshots are generated serializing results of type T to a file using the ostream& operator<< (T…
Alessandro Pezzato
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How to write a formatter for fmt using wchar_t?

I want to specialize a formatter template so I can write: rect rc(0, 0, 100, 20); wstring buf = fmt_msg(L"{0}", rc); I have this: ea::wstring vfmt_msg(const ea::wstring &msg, fmt::wformat_args args) { std::wstring s_ =…
Mark Kosyk
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How to get fmt::format to work with wchar_t?

I want to have fmt::format return a wstring from EA's STL, but when I try to modify this code from the docs—which works fine: // Prints formatted error message. void vreport_error(const char *format, fmt::format_args args) { fmt::print("Error:…
Mark Kosyk
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Issue on using {fmt} as a dependency with CMake

I'm trying to apply modern CMake practices in my project. And I've came up with an issue with the {fmt} library dependency. The structure of a project is the following (in a brief): dev/ | +--- fmt/ *unpacked archive of 4.1.0 version* | +---…
kola
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