Question

I have a format string like this:

buf[] = "A%d,B%d,C%d,D%d,F%d,G%d,H%d,I%d,J%d";

and I want to insert the same integer for each %d so I use:

 int val = 6;
 sprintf(buf2, buf, val,val,val,val,val,val,val,val,val);

Can I use sprintf in a way that only requires me to write val once, and sprintf will use it for each %d?

Answer 1

Yes, you can use %1$d everytime. The 1$ references the second argument, you could obviously do it with other arguments, too.

Demo: http://codepad.org/xVmdJkpN

Note that the position specifier is a POSIX extension – so it might not work with every single compiler. If you need it to work e.g. with the Visual C++ compiler, consider using the ugly way of repeating the argument or do not use a printf-style function at all. Another option would be using a POSIX-compatible sprintf implementation or using multiple calls to append one number everytime in a loop (in case the format string is built dynamically which would prevent you from specifying the correct number of arguments).

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On a side-note, sprintf should be avoided. Use snprintf(buf2, sizeof(buf2), ....) instead. Of course this requires buf2 to have a static size known at compile-time – but if you allocate it manually you can simply use the variable containing the length instead of sizeof(buf2).