Can you specify variable field width in scanf format string?

Answer 1

Answer

You can't specify a variable field with a fixed format string, but you can get around this by making the format string variable:

int width; char format[20]; /* or whatever size is appropriate */ int value; ... sprintf(format, "%%%dd", width); /* generates a string like "%5d" */ scanf(format, &value);

The only drawback to this method, other than requiring two statements, is that the compiler can't do a sanity check on the arguments to scanf like it can when the format is a string constant.

Answer

If you want to specify a variable width in a printf format string (as opposed to scanf), you can do the following:

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

That will use the value of "width" as the width for formatting the value of "num" as a decimal integer.

Answer 2

Yes, you can specify variable width, however you can't specify precision. The format tags are as follows:

scanf: %[*][width][length]type

printf: %[*][width][.precision][length]type

As you can see, scanf lacks the precision tag but does include the length tag.

See: http://msdn2.microsoft.com/en-us/library/kwwtf9ch.aspx

Answer 3

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