如何在指定的初始化程序中引用参数？

Question

我想将一个参数的值添加到指定初始值设定项中的另一个参数，而无需定义单独的变量来保存该值。这可能吗？

typedef struct {
  int x;
  int y;
} point;

int main() {
  point p = {
    .x = 1,
    .y = x + 2 // I want to reference .x
  };
}

Answer 1

这是不可能的。初始化器中表达式的求值顺序不会以任何特定顺序求值，因此无法保证 .x 会在 .y 设置为 .x + 2.[=16= 之前设置为 1 ]

这在 C standard 的第 6.7.9p23 节中有详细说明：

The evaluations of the initialization list expressions are indeterminately sequenced with respect to one another and
thus the order in which any side effects occur is unspecified.¹⁵²⁾

脚注 152 指出：

In particular, the evaluation order need not be the same as the order of subobject initialization.

如何在指定的初始化程序中引用参数？

How can I reference a parameter within a designated initializer?

c

designated-initializer