C语言中“复杂"的默认类型 [英] Default types for 'complex' in C

问题描述

根据我阅读的文档C99，以后将float complex，double complex和long double complex作为复杂类型支持.但是，使用gcc -Wall -Wextra时，该代码将编译而不会发出警告.

According the docs I have read C99 and later support float complex, double complex and long double complex as complex types. However this code compiles without warning when using gcc -Wall -Wextra.

#include <stdio.h>
#include <complex.h>

int main() {
    int a, b, c, d;
    float re, im;

    scanf("%d %d", &a, &b);
    complex matrix[a][b]; /* <------ */

    for(c=0; c<a; c++) {
        for(d=0; d<b; d++) {
            scanf("%f%fi", &re, &im);
            matrix[c][d] = re + im * I;
        }
    }

    for(c=0; c<a; c++) {
        for(d=0; d<b; d++) {
            printf("%.2f%+.2fi ", creal(matrix[c][d]), cimag(matrix[c][d]));
        }
        printf("\n");
    }
}

• 这是有效的C还是gcc的奇数?
• complex matrix[a][b];给我们的是什么类型?
• Is this valid C or is it a gcc oddity?
• What type is complex matrix[a][b]; giving us?

如果使用clang进行编译，则会得到:

If you compile it with clang you get:

main.c:9:5:警告:普通的'_Complex'需要类型说明符； 假设为"_Complex double"

main.c:9:5: warning: plain '_Complex' requires a type specifier; assuming '_Complex double'

请参见 clang输出.

gcc错误现已在此链接中报告. (不是我的.)

gcc bug now reported at this link. (Not by me.)

推荐答案

如果您忽略了GCC和Clang，则假定类型为double(例如您的示例). lang产生:

Looks like both GCC and Clang assume the type to be double if you omit it (like in your example). Clang produces:

 warning: plain '_Complex' requires a type specifier; assuming '_Complex double'
    complex matrix[a][b];
    ^
            double
/usr/include/complex.h:39:18: note: expanded from macro 'complex'
#define complex         _Complex
                        ^

尽管GCC做了同样的事情(假设double)，但似乎没有发出警告.

While does GCC does the same (assuming double), it doesn't seem to warn it.

无论编译器如何诊断，扩展到_Complex的complex本身都不是 type ，而仅仅是 type指示符.因此，您需要指定类型.

Regardless of compiler diagnostics, complex which expands to _Complex is not a type by itself but only a type specifier. So, you need to specify the type.

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