如何避免在多态打印宏中使用#if [英] how can I avoid the use of #if in a polymorphic print macro

问题描述

让我们尝试运行以下代码:

Let's try to run the following code:

#include <stdio.h>
#define MY_MACRO1(isArray,y) do { \
                      if(isArray) \
                        printf("%d", y[0]); \
                      else \
                        printf("%d", y); \
                     }while(0)

int main()
{
    int a = 38;
    int b[]={42};

    MY_MACRO1(0,a);

    return 0;
}

它返回错误:

main.c: In function ‘main’:
main.c:12:39: error: subscripted value is neither array nor pointer nor vector
                         printf("%d", y[0]); \

好的，因此仅当变量是数组时，我们才需要#if语句来运行y [0]:

Ok, so we would need a #if statement to run y[0] only if the variable is an array:

#define MY_MACRO2(isArray,y) do { \
                      #if isArray \
                      printf("%d", y[0]); \
                      #else \
                      printf("%d", y); \
                      #endif \
                     }while(0)

int main()
{
    int a = 38;
    int b[]={42};

    MY_MACRO2(0,a);

    return 0;
}

但是它返回:

main.c:11:28: error: '#' is not followed by a macro parameter
 #define MY_MACRO2(isArray,y) do { \

总有没有在宏中调用#if语句? 如果没有，我该怎么做?

Is there anyway to call a #if statement inside a macro? if not, how can I do such a thing?

注意:我使用的是IAR 8.20.2

note: I'm using IAR 8.20.2

(此链接没有帮助)

我想知道为什么我不想使用2个不同的宏是因为我需要这样的东西(伪代码):

I you want to know why I would not like to use 2 different macros is because I need to to something like this (pseudo-code):

myFunction(int or array):
   doSomethingWhereIntAndArrayBehavesDifferentlyLikePrintf();
   doSomethingelse();
   doSomethingelse();
   doSomethingWhereIntAndArrayBehavesDifferentlyLikePrintf();
   doSomethingelse();

• 这非常方便:您可以分解代码.
• 这是一种实现多态的方法.
• 它模仿C ++模板功能.

推荐答案

反正在宏内调用#if语句吗?

Is there anyway to call a #if statement inside a macro?

不可能.

如果没有，我该怎么做?

if not, how can I do such a thing?

您可以使用C11 _Generic:

You could use C11 _Generic:

#include <stdio.h>

void int_func (int obj)
{
  printf("%d\n", obj);
}

void int_arr_func (const int* obj)
{
  printf("%d\n", obj[0]);
}

void float_func (float obj)
{
  printf("%f\n", obj);
}

#define MY_MACRO2(y) _Generic((y), \
  int:   int_func,                 \
  int*:  int_arr_func,             \
  float: float_func ) (y)


int main (void)
{
    int a = 38;
    int b[]={42};
    float pi = 3.14f;

    MY_MACRO2(a);
    MY_MACRO2(b);
    MY_MACRO2(pi);
    return 0;
}

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