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8.8 Replacement for Stdio Formatting Library

Using the ‘printf’ formatting routines in a portable fashion has always been a pain, and this package has been way more pain than anyone ever imagined. Hopefully, with this release of snprintfv, the pain is now over for all time.

The issues with portable usage are these:

1. Argument number specifiers are often either not implemented or are buggy. Even GNU libc, version 1 got it wrong.
2. ANSI/ISO "forgot" to provide a mechanism for computing argument lists for vararg procedures.
3. The argument array version of printf (‘printfv()’) is not generally available, does not work with the native printf, and does not have a working argument number specifier in the format specification. (Last I knew, anyway.)
4. You cannot fake varargs by calling ‘vprintf()’ with an array of arguments, because ANSI does not require such an implementation and some vendors play funny tricks because they are allowed to.

These four issues made it impossible for AutoGen to ship without its own implementation of the ‘printf’ formatting routines. Since we were forced to do this, we decided to make the formatting routines both better and more complete :-). We addressed these issues and added the following features to the common printf API:

5. The formatted output can be written to
   • a string allocated by the formatting function (‘asprintf()’).
   • a file descriptor instead of a file stream (‘dprintf()’).
   • a user specified stream (‘stream_printf()’).
6. The formatting functions can be augmented with your own functions. These functions are allowed to consume more than one character from the format, but must commence with a unique character. For example,

   "%{struct stat}\n"
   

   might be used with ’{’ registered to a procedure that would look up "struct stat" in a symbol table and do appropriate things, consuming the format string through the ’}’ character.

Gary V. Vaughan was generous enough to supply this implementation. Many thanks!!

For further details, the reader is referred to the snprintfv documentation. These functions are also available in the template processing as ‘sprintf’ (see SCM sprintf), ‘printf’ (see SCM printf), ‘fprintf’ (see SCM fprintf), and ‘shellf’ (see SCM shellf).