Using sprintf without a manually allocated buffer

Question

In the application that I am working on, the logging facility makes use of sprintf to format the text that gets written to file. So, something like:

char buffer[512];
sprintf(buffer, ... );

This sometimes causes problems when the message that gets sent in becomes too big for the manually allocated buffer.

Is there a way to get sprintf behaviour without having to manually allocate memory like this?

EDIT: while sprintf is a C operation, I'm looking for C++ type solutions (if there are any!) for me to get this sort of behaviour...

Answer 1

You can use asprintf(3) (note: non-standard) which allocates the buffer for you so you don't need to pre-allocate it.

Answer 2

No you can't use sprintf() to allocate enough memory. Alternatives include:

• use snprintf() to truncate the message - does not fully resolve your problem, but prevent the buffer overflow issue
• double (or triple or ...) the buffer - unless you're in a constrained environment
• use C++ std::string and ostringstream - but you'll lose the printf format, you'll have to use the << operator
• use Boost Format that comes with a printf-like % operator