Question

#include <stdio.h>
#define all_mem (sizeof(x) /sizeof(x[0]))
int x[] ={1,2,3,4,5,6,7,8,9,10};

     int main(void) {
            //  printf("The condition is %d",(all_mem-2));
            int i;
                for(i=-1;i<=(all_mem-2);i++)
            {
                printf("The number is %d",i);
            }
            return 0;
        }

在上面的循环代码中甚至没有执行一次，我尝试了打印条件并且它满足循环条件。任何见解如何将for循环条件中的宏表达式计算为小于-1的值？

Answer 1

find / -iname abc.[]宏返回all_mem值;整数提升规则意味着size_t正在推广i <= (all_mem - 2)到i的比较，这意味着价值很大，而不是size_t。尝试投射以确保签名比较：

-1

Answer 2

对代码进行一些更正后，forofance，sizeof（）返回size_t，而不是int代码完美无缺。

以下是修改后的代码：

#include <stdio.h>

#define all_mem (sizeof(x) /sizeof(x[0]))

int x[] ={1,2,3,4,5,6,7,8,9,10};

int main(void)
{
    printf( "all_mem = %ld\n", all_mem ); // << added for debugging

    //  printf("The condition is %d",(all_mem-2));
    int i;
        for(i=-1;i<=(int)(all_mem-2);i++) // << 
        // << properly cast to int
        // otherwise compiler raises warning and unsigned comparison made
    {
        printf("The number is %d\n",i);
    }
    return 0;
}

以下是上述代码的输出：

all_mem = 10
The number is -1
The number is 0
The number is 1
The number is 2
The number is 3
The number is 4
The number is 5
The number is 6
The number is 7
The number is 8

编译时，始终启用所有警告，然后修复这些警告。

如果遵循上述陈述，那么在没有我们帮助的情况下你会看到问题。

（对于gcc，至少使用：-Wall -Wextra -pedantic并且我还添加：-Wconversion -std=c99）

对于循环条件

2 个答案: