sscanf 中 uint16_t 的正确且可移植的 (Clang/GCC) 修饰符是什么？

Question

当我尝试编译此代码时收到一条警告消息 sscanf(value, "%h" PRIu16 "B", &packet_size) 使用 Clang 600.0.57 (OS X)。

warning: format specifies type 'unsigned char *' but the argument has type 'uint16_t *'
      (aka 'unsigned short *') [-Wformat]
    if (sscanf(value, "%h" PRIu16 "B", &packet_size) == 1) {
                       ~~~~            ^~~~~~~~~~~~

但是如果我删除修饰符“h”，那么我会在 GCC 4.8.3 (Scientific Linux 7) 中收到以下错误。

warning: format ‘%u’ expects argument of type ‘unsigned int*’, but argument 3 has type ‘uint16_t* {aka short unsigned int*}’ [-Wformat=]
     if (sscanf(value, "%" PRIu16 "B", &packet_size) == 1) {

                                                   ^

什么是 sscanf 中 uint16_t* 的正确且可移植的修饰符？

=== 在下面添加了更多不言自明的示例 ===

test.c

#ifndef __STDC_FORMAT_MACROS
#define __STDC_FORMAT_MACROS 1
#endif
#include <inttypes.h>
#include <stdio.h>

int main() {
  char* str = "16 bits";
  uint16_t u16;
  sscanf(str, "%h" PRIu16 " bits", &u16); // Clang warning
  sscanf(str, "%" PRIu16 " bits", &u16); // GCC warning
  sscanf(str, "%" SCNu16 " bits", &u16); // OK for both compilers

  printf("%" PRIu16 " bits\n", u16);

  return 0;
}

Clang 警告

$ clang test.c -Wall -Wextra
test.c:10:36: warning: format specifies type 'unsigned char *' but the argument
      has type 'uint16_t *' (aka 'unsigned short *') [-Wformat]
  sscanf(str, "%h" PRIu16 " bits", &u16); // Clang warning
               ~~~~                ^~~~
1 warning generated.

GCC 警告

$ gcc -Wall -Wextra test.c
test.c: In function ‘main’:
test.c:11:3: warning: format ‘%u’ expects argument of type ‘unsigned int *’, but argument 3 has type ‘uint16_t *’ [-Wformat=]
   sscanf(str, "%" PRIu16 " bits", &u16); // GCC warning
   ^

Answer 1

正如@EOF 在他们的评论中所说，fscanf 和 fprintf 都有自己的宏。

在final C99 draft 中，§7.8.1 第 4 和 5 条（第 199 页）说<inttypes.h> 应定义以下宏：

4. 有符号整数的fscanf 宏是：

   SCNdN SCNdLEASTN SCNdFASTN SCNdMAX SCNdPTR
   SCNiN SCNiLEASTN SCNiFASTN SCNiMAX SCNiPTR

5. 用于无符号整数的fscanf 宏是：

   SCNoN SCNoLEASTN SCNoFASTN SCNoMAX SCNoPTR
   SCNuN SCNuLEASTN SCNuFASTN SCNuMAX SCNuPTR
   SCNxN SCNxLEASTN SCNxFASTN SCNxMAX SCNxPTR

如果您想将uint16_t 与fscanf 一起读取为十进制数字，则必须使用SCNu16。

例子：

#include <inttypes.h>
#include <stdint.h>
#include <stdio.h>

int main(void) {
    uint16_t input;

    int items = scanf("fetch %" SCNu16 " bits", &input);

    if (items == 1) {
        printf("I'm busy, go fetch those %" PRIu16 " bits yourself.\n", input);
    } else {
        printf("I don't understand what you're saying.\n")
    }

    return 0;
}