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GNU autosprintf, version 1.0

Formatted Output to Strings in C++

Bruno Haible


Table of Contents


1 Introduction

This package makes the C formatted output routines (fprintf et al.) usable in C++ programs, for use with the <string> strings and the <iostream> streams.

It allows to write code like

cerr << autosprintf ("syntax error in %s:%d: %s", filename, line, errstring);

instead of

cerr << "syntax error in " << filename << ":" << line << ": " << errstring;

The benefits of the autosprintf syntax are:

  • It reuses the standard POSIX printf facility. Easy migration from C to C++.
  • English sentences are kept together.
  • It makes internationalization possible. Internationalization requires format strings, because in some cases the translator needs to change the order of a sentence, and more generally it is easier for the translator to work with a single string for a sentence than with multiple string pieces.
  • It reduces the risk of programming errors due to forgotten state in the output stream (e.g. cout << hex; not followed by cout << dec;).

2 The autosprintf class

An instance of class autosprintf just contains a string with the formatted output result. Such an instance is usually allocated as an automatic storage variable, i.e. on the stack, not with new on the heap.

The constructor autosprintf (const char *format, ...) takes a format string and additional arguments, like the C function printf.

Conversions to char * and std::string are defined that return the encapsulated string.

The destructor ~autosprintf () destroys the encapsulated string.

An operator << is provided that outputs the encapsulated string to the given ostream.

3 Using autosprintf in own programs

To use the autosprintf class in your programs, you need to add

#include "autosprintf.h"
using gnu::autosprintf;

to your source code. The include file defines the class autosprintf, in a namespace called gnu. The `using´ statement makes it possible to use the class without the (otherwise natural) gnu:: prefix.

When linking your program, you need to link with libasprintf, because that's where the class is defined. In projects using GNU autoconf, this means adding `AC_LIB_LINKFLAGS([asprintf])´ to configure.in or configure.ac, and using the @LIBASPRINTF@ Makefile variable that it provides.


This document was generated on 12 June 2003 using the texi2html translator version 1.52a.