C语言:initializer element is not constant
2017-08-29 14:16
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static struct QueuePtr * header =( ( struct QueuePtr * ) malloc(sizeof(struct QueuePtr ) ) );在编译时报错:initializer element is not constant
原因:在c99中指明全局变量和static变量的初始化式必须为常量表达式
修改:
static struct QueuePtr * header = NULL; header = ( ( struct QueuePtr * ) malloc(sizeof(struct QueuePtr ) ) );
查阅其他博客,看到以下代码也会报同样的错误:
链接:为什么出现“initializer element is not constant”错误
#include <stdio.h> int a = 1; int b = 2; int c = a+b; int main() { printf("c is %d\n", c); return 0; }同理,上述代码中全局变量c的值是在执行时才确定的。全局变量的初始化是在编译阶段完成的,因此不可以是尚未确定其值的变量。
(1)c语言中全局变量和static变量的初始化需要指定一个常量,不能是一个非常量的表达式;
(2)作为全局变量,在编译之后就要确定它的地址,如果这个全局变量是个结构体的话,那么结构体里面的各个成员的具体值也要确定了。因为全局变量是存储在静态区,而只有常量表达式才可以前期确定值,而不是具体运行时确定值。
(3)依据:
C99标准 6.7.8 Initialization 第4款:
4 All the expressions in an initializer for an object that has static storage duration shall be constant expressions or string literals.
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