c变量范围

Question

如果在块中定义了变量,它是仅存在于块中还是整个程序中？例如

main()
{
    int j=5;
    {
        int i=10
        printf("%d",i);
    }
    printf("%d , %d ",i,j);
}

它有效吗？

main()
{
    int j=5, *k;
    {
        int i=10
        printf("%d",i);
    }
     k=&i
    printf("%d , %d ",*k,j);
}

因为变量保留在内存中从它的声明点到函数退出点？

Answer 1

非全局变量的作用域仅限于它定义的块.此外,对于自动变量,一旦块结束,变量的生命周期就结束了.

考虑这个愚蠢的例子:

void doit()
{
    int *ps;
    int *pa;

    {
        static int s = 1;
        int a = 2;

        ps = &s;
        pa = &a;
    }

    // cannot access a or s here because they are out of scope
    // *ps is okay because s is static so it's lifetime is not over
    // *pa is not okay because a's lifetime ends at the end of the block
}

您的第二个printf行将无法编译,因为i它不在范围内.