How can I specify a variable width in a scanf format string?
How can I specify a variable width in a scanf format string?
✍: Guest
You can't; an asterisk in a scanf format string means to suppress assignment. You may be able to use ANSI stringizing and string concatenation to construct a constant format specifier based on a preprocessor macro containing the desired width:
#define WIDTH 3
#define Str(x) #x
#define Xstr(x) Str(x) /*
scanf("%" Xstr(WIDTH) "d", &n);
If the width is a run-time variable, though, you'll have to build the format specifier at run time, too:
char fmt[10];
sprintf(fmt, "%%%dd", width);
scanf(fmt, &n);
(scanf formats like these are unlikely when reading from standard input, but might find some usefulness with fscanf or sscanf.)
2015-10-26, 1391👍, 0💬
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