Specifying the maximum string length to scanf dynamically in C (like “%*s” in printf)

Question

I can specify the maximum amount of characters for scanf to read to a buffer using this technique:

char buffer[64];

/* Read one li         


        

Answer 1

There is indeed no variable width specifier in the scanf family of functions. Alternatives include creating the format string dynamically (though this seems a bit silly if the width is a compile-time constant) or simply accepting the magic number. One possibility is to use preprocessor macros for specifying both the buffer and format string width:

#define STR_VALUE(x) STR(x)
#define STR(x) #x

#define MAX_LEN 63

char buffer[MAX_LEN + 1];
fscanf(file, "%" STR_VALUE(MAX_LEN) "[^\n]", buffer);