confusion about short data type format specifier in C

问题

Consider following program:

#include <stdio.h>
int main()
{
    short a=9;
    //printf("%hi\n",a);
    printf("%d",a);  // LINE 6
}

According to this the format specifier for short type (signed) is %hi Is the short type variable always gets promoted automatically to int before performing any operation on it? Is it undefined behavior , If I use %d format specifier to print the value of variable in this program? I compiled it using gcc -Wall -Wextra -WFormat options but still compiler isn't showing any single warning. Why?

回答1:

printf("%hi\n", a);

a is promoted to int as per the rules of default argument promotion of variadic functions.

Anyway as you use h specifier the implementation is allowed to expect the int value is within SHRT_MIN or SHRT_MAX limits. Passing a value outside the bounds is undefined behavior.

Of course printf("%i\n", a); is also valid because of the int promotion of a so using %hi conversion specification is not very usual.

来源：https://stackoverflow.com/questions/32528580/confusion-about-short-data-type-format-specifier-in-c