GNU autosprintf, version 1.0

Formatted Output to Strings in C++

Bruno Haible

Table of Contents

Copyright (C) 2002-2003, 2006-2007 Free Software Foundation, Inc.

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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:

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 conversion to char * returns a freshly allocated copy of the encapsulated string; it needs to be freed using delete[]. The conversion to std::string returns a copy of the encapsulated string, with automatic memory management.

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 or, and using the @LIBASPRINTF@ Makefile variable that it provides.

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