I've got:

#define WIDTH 10

and I want to use it in the format string for a scanf() call.  Using:

int i;

[...]

scanf( "%WIDTHd", &i );

doesn't seem to work, but:

int i;

[...]

scanf( "%10d", &i );

works fine.

What am I doing wrong?

If you could, please send any reply to:

Todd Krissel

|#define WIDTH 10
|
|and I want to use it in the format string for a scanf() call.  Using:
|
|int i;
|scanf( "%WIDTHd", &i );
|
|doesn't seem to work, but:
|
|int i;
|
|scanf( "%10d", &i );
|
|works fine.
|What am I doing wrong?

Unlike the printf() function which can read its width and precision
specifiers from its argument list (by sticking in a `*' where the
width/precision is expected), scanf can't do this. (a `*' causes the
scanf() function to suppress assignment to the corresponding argument.)

But who cares? a `%d' format specifier causes the scanf() function
to skip any leading white space before it attempts to read a decimal
integral number. A simple `%d' format specifier makes scanf() read
strings like `123', `    123'or `        123', etc. correctly.

If you _really_ insist doing this, you have to compose the format
string yourself. Something like this'll do:

        char buf[ENOUGH_CHARS];
        int  i;

        sprintf(buf, "%%%dd", WIDTH);
        scanf(buf, &i);

(please note the double `%%'; it cause the sprintf() function to
output a single `%' character.)

kind regards,

----------------------------------------------------------------------------
Doc, I wanted to talk to you about my problem with premature ... *whoops*

1. The preprocessor doesn't expand macros inside strings.

2. Even outside strings, WIDTHd is _not_ a macro and the preprocessor is
not allowed to touch it.

You can use the '#' preprocessing operator to solve your problem, but the
solution is rather tricky. It is described in the comp.lang.c FAQ.

Dan
--
Dan Pop
Tel:   +41.22.767.5712

Mail:  CERN - PPE, Bat. 31 R-004, CH-1211 Geneve 23, Switzerland