scanf() variable length specifier

Question

How can I use a variable to specify the max number of chars scanf() should read in?

For example using printf() you can use the * like so

Answer 1

Kernighan and Pike recommend using snprintf() to create the format string. I developed this idea into a method that safely reads strings:

void scan_string(char * buffer, unsigned length) {
    char format[12]; // Support max int value for the format %s
    snprintf(format, sizeof(format), "%%%ds", length - 1); // Generate format
    scanf(format, buffer);
}

int main() {
  char string[5];
  scan_string(string, sizeof(string));
  printf("%s\n", string);
}