c - 为什么 GCC 只提示在给出 -pedantic 时将 unsigned int 参数与 %i 一起使用？

Question

sscanf(3) 说(强调我的):

i
Matches an optionally signed integer; the next pointer must be a pointer to int. The integer is read in base 16 if it begins with 0x or 0X, in base 8 if it begins with 0, and in base 10 otherwise. Only characters that correspond to the base are used.

然而 GCC 并没有提示使用 unsigned int与 %i除非 -pedantic给出。这与我习惯的行为不同，其中 GCC 会警告任何不匹配的类型和格式字符串。

为什么这种组合表现不同？

鉴于此警告未包含在常见的 -Wall 中一组警告，是否可以通过 unsigned int至 %i ?

示例程序:

#include <stdio.h>

int main(void)
{
    int i;
    unsigned int u;
    float f;

    scanf("%i", &i);
    scanf("%i", &u);
    scanf("%i", &f);

    return 0;
}

无 -pedantic , GCC 投诉 %i和 float * ，但不是 unsigned int * :

$ gcc -Wall -Wextra scanf_i.c 
scanf_i.c: In function ‘main’:
scanf_i.c:11:13: warning: format ‘%i’ expects argument of type ‘int *’, but argument 2 has type ‘float *’ [-Wformat=]
     scanf("%i", &f);
            ~^   ~~
            %e

与 -pedantic , GCC 提示两者:
输出 -pedantic :

$ gcc -Wall -Wextra -pedantic scanf_i.c 
scanf_i.c: In function ‘main’:
scanf_i.c:10:13: warning: format ‘%i’ expects argument of type ‘int *’, but argument 2 has type ‘unsigned int *’ [-Wformat=]
     scanf("%i", &u);
            ~^   ~~
            %i
scanf_i.c:11:13: warning: format ‘%i’ expects argument of type ‘int *’, but argument 2 has type ‘float *’ [-Wformat=]
     scanf("%i", &f);
            ~^   ~~
            %e

海湾合作委员会版本:

$ gcc --version
gcc (Debian 8.3.0-6) 8.3.0

Answer 1

-Wformat-signedness控制当参数类型仅在符号性与预期不同时是否引发警告。

来自 gcc(1) man page :

-Wformat-signedness
If -Wformat is specified, also warn if the format string requires an unsigned argument and the argument is signed and vice versa.

手册页没有明确说明此标志包含在 -pedantic 中。 , ( -Wpedantic ) 但它确实说:

However, if -Wpedantic is used with -Wformat, warnings are given about format features not in the selected standard version.