Set variable text column width in printf

You can do this as follows:

printf("%*d", width, value);

From Lee's comment:
You can also use a * for the precision:

printf("%*.*f", width, precision, value);

Note that both width and precision must have type int as expected by printf for the * arguments, type size_t is inappropriate as it may have a different size and representation on the target platform.

Just for completeness, wanted to mention that with POSIX-compliant versions of printf() you can also put the actual field width (or precision) value somewhere else in the parameter list and refer to it using the 1-based parameter number followed by a dollar sign:

A field width or precision, or both, may be indicated by an asterisk ‘∗’ or an asterisk followed by one or more decimal digits and a ‘$’ instead of a digit string. In this case, an int argument supplies the field width or precision. A negative field width is treated as a left adjustment flag followed by a positive field width; a negative precision is treated as though it were missing. If a single format directive mixes positional (nn$) and non-positional arguments, the results are undefined.

E.g., printf ( "%1$*d", width, value );