在switch case中使用指针值。 [英] Using a pointer value in switch case.

问题描述

#include <stdio.h>
int main() {
	//code
	int i=5;
	int *p=&i;
	printf ("%d", *p);
	switch (*p)
	{
	    case *p:
                printf ("&&");
                break;
	}
	return 0;
}

* p给出i的值。那么为什么这个程序会出错呢？



我尝试了什么：



Switch语句适用于整数表达式，而指针不是整数表达式。但是我传递了指针指向的值为5.那么这不应该运行吗？

*p gives value of i. Then why is this program running into error?

What I have tried:

Switch statement works on integral expressions and pointer is not an integral expression. But i am passing the value pointed by the pointer that is 5. So should this not run?

推荐答案

Quote：

在开关盒中使用指针值。

Using a pointer value in switch case.

简答：对于你想要的，它是如果结构，不是switch。

Short answer: For what you want, it is if structure, not switch.

到目前为止，这个开关（* p）还可以。但是这个案例* p：就是问题所在。

为什么？

在c中查看Switch语句的定义，例如：这里：切换声明（C） [ ^ ]

定义说大小写常量-expression：表示你需要为case部分使用常量Expression，而 * p 是一个（解除引用的指针）变量，因此不允许在这里。



我希望这会有所帮助。

This one switch (*p) is ok so far. But this one case *p: is the Problem.
Why?
Have a look to the Definition of the Switch Statement in c, e.g. here: switch Statement (C)[^]
The Definition says case constant-expression : and means you Need to use a constant Expression for the "case part", while *p is a (dereferenced pointer) variable and therefore not allowed here.

I hope this helps.

来自在C中切换语句 [ ^ ]

From switch statement in C[^]

Quote：

以下规则适用转换语句



- switch语句中使用的表达式必须具有整数或枚举类型，或者是w中的类类型该类具有单个转换函数为整数或枚举类型。



- 您可以在一个开关中包含任意数量的case语句。每个案例后跟要比较的值和冒号。



- 案例的常量表达式必须与变量中的变量相同。切换，它必须是常量或字面值。



- 当接通的变量等于大小写时，该情况后的语句将执行，直到a达到break语句。



- 当达到break语句时，开关终止，控制流跳转到switch语句后的下一行。 />


- 并非每个案例都需要包含休息时间。如果没有出现中断，控制流将落到后续情况，直到达到中断。



- switch语句可以有一个可选的默认情况，必须出现在开关的末尾。当没有任何情况属实时，默认情况可用于执行任务。在默认情况下不需要中断。

The following rules apply to a switch statement

- The expression used in a switch statement must have an integral or enumerated type, or be of a class type in which the class has a single conversion function to an integral or enumerated type.

- You can have any number of case statements within a switch. Each case is followed by the value to be compared to and a colon.

- The constant-expression for a case must be the same data type as the variable in the switch, and it must be a constant or a literal.

- When the variable being switched on is equal to a case, the statements following that case will execute until a break statement is reached.

- When a break statement is reached, the switch terminates, and the flow of control jumps to the next line following the switch statement.

- Not every case needs to contain a break. If no break appears, the flow of control will fall through to subsequent cases until a break is reached.

- A switch statement can have an optional default case, which must appear at the end of the switch. The default case can be used for performing a task when none of the cases is true. No break is needed in the default case.

我认为你的指针不符合规则第一。

I think your pointer is not fitting in rule number one.

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