strformat

A lightweight, header-only string formatting library for C++ that provides printf-style formatting with a fluent, chainable API.

Overview

strformat is a modern C++ string formatting library that:

• Is header-only for simple integration
• Provides printf-style format specifiers
• Uses method chaining for a clean API
• Supports cross-platform development (Windows, Linux)
• Offers locale-independent formatting
• Supports formatting of integers, floating-point numbers, characters, strings, and pointers
• Handles width, precision, alignment, and padding options

Requirements

• C++17 compatible compiler
• No external dependencies

Getting Started

Simply include the strformat.h header file in your project:

#include"strformat.h"

Basic Usage

#include"strformat.h"
#include<iostream>intmain() {
// Format to string
std::string result = fmt("Hello, %s! The answer is %d.")
.s("world")
.d(42)
.str();
std::cout << result << std::endl;
// Direct output to stdoutfmt("Hello, %s! The answer is %d.")
.s("world")
.d(42)
.put();
// Direct output to stderrfmt("Error code: %d").d(-1).err();
return0;
}

Format Specifiers

strformat supports the following format specifiers:

• %d - 32-bit signed integer
• %ld - 64-bit signed integer
• %u - 32-bit unsigned integer
• %lu - 64-bit unsigned integer
• %f - Floating-point number
• %s - String
• %c - Character
• %x - Hexadecimal (lowercase)
• %X - Hexadecimal (uppercase)
• %o - Octal
• %p - Pointer

Formatting Options

Various formatting options are available:

// Width and paddingfmt("%10d").d(123); // " 123"fmt("%010d").d(123); // "0000000123"fmt("%-10d").d(123); // "123 "// Sign controlfmt("%+d").d(123); // "+123"// Precision for floating-point numbersfmt("%.2f").f(123.456); // "123.46"// Combined optionsfmt("%+10.2f").f(123.456); // " +123.46"

Method Chaining

You can chain multiple formatting operations:

std::string result = fmt("Name: %s, Age: %d, Balance: $%.2f")
.s("John Doe")
.d(35)
.f(1234.567)
.str();

Output Options

strformat provides several output options:

// Get as string
std::string result = fmt("Value: %d").d(123).str();
// Write to stdoutfmt("Value: %d").d(123).put();
// Write to stderrfmt("Error: %d").d(123).err();
// Write to a FILE pointerFILE* fp = fopen("output.txt", "w");
fmt("Value: %d").d(123).write_to(fp);
fclose(fp);
// Write to a file descriptorfmt("Value: %d").d(123).write_to(fd);
// Get as vector
std::vector<char> buffer = fmt("Value: %d").d(123).vec();
// Append to a vectorfmt("Value: %d").d(123).append_to(&buffer);

Build Options

To disable floating-point support (for smaller footprint):

#defineSTRFORMAT_NO_FP
#include"strformat.h"

To disable locale support:

#defineSTRFORMAT_NO_LOCALE
#include"strformat.h"

Building the Project

Linux

# Using make
make
# Using qmake
./mk.sh
cd _build
make

Windows

Open the Visual Studio solution file strformat.sln and build the project.

License

This software is distributed under the MIT license.

Copyright (C) 2025 S.Fuchita (soramimi_jp)