scanf / field lengths : using a variable / macro, C/C++

Question

How can I use a variable to specify the field length when using scanf. For example:

char word[20+1];
scanf(file, \"%20s\", word);

Also, is

Answer 1

If you're using regular scanf (Linux), you have two solutions :

#define MAX_STRING_LENGTH_STR "20"
scanf(file, "%"MAX_STRING_LENGTH_STR"s", word);

OR

#define MAX_STRING_LENGTH 20
sprintf(format, "%%%ds", MAX_STRING_LENGTH);
scanf(file, format, word);

However, it seems to be use this code with Visual Studio :

char str[21];
scanf("%20s", str, 21);