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>

int main() {
    // Format to string
    std::string result = strf("Hello, %s! The answer is %d.")
                        .s("world")
                        .d(42)
                        .str();
    std::cout << result << std::endl;
    
    // Direct output to stdout
    strf("Hello, %s! The answer is %d.")
        .s("world")
        .d(42)
        .put();
        
    // Direct output to stderr
    strf("Error code: %d").d(-1).err();
    
    return 0;
}

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 padding
strf("%10d").d(123);       // "       123"
strf("%010d").d(123);      // "0000000123"
strf("%-10d").d(123);      // "123       "

// Sign control
strf("%+d").d(123);        // "+123"

// Precision for floating-point numbers
strf("%.2f").f(123.456);   // "123.46"

// Combined options
strf("%+10.2f").f(123.456); // "    +123.46"

Method Chaining

You can chain multiple formatting operations:

std::string result = strf("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 = strf("Value: %d").d(123).str();

// Write to stdout
strf("Value: %d").d(123).put();

// Write to stderr
strf("Error: %d").d(123).err();

// Write to a FILE pointer
FILE* fp = fopen("output.txt", "w");
strf("Value: %d").d(123).write_to(fp);
fclose(fp);

// Write to a file descriptor
strf("Value: %d").d(123).write_to(fd);

// Append to a vector
std::vector<char> buffer;
strf("Value: %d").d(123).vec(&buffer);

Build Options

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

#define STRFORMAT_NO_FP
#include "strformat.h"

To disable locale support:

#define STRFORMAT_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)