“引用”和“解除引用”的含义

问题描述 投票:51回答:6

我在互联网上阅读不同的东西并感到困惑,因为每个网站都说不同的东西。

谈到C.

我读到了*引用运算符和&解除引用运算符;或者引用意味着使指针指向变量,并且解除引用正在访问指针指向的变量的值。所以我很困惑。

我是否可以获得有关“引用和取消引用”的简单但彻底的解释?

c pointers reference dereference
6个回答
73
投票

引用意味着获取现有变量的地址(使用&)来设置指针变量。为了有效,必须将指针设置为与指针相同类型的变量的地址,而不是星号:

int  c1;
int* p1;
c1 = 5;
p1 = &c1;
//p1 references c1

取消引用指针意味着使用*运算符(星号字符)从指针指向的内存地址中检索值:注意:存储在指针地址处的值必须是值相同类型作为类型变量指针“指向”,但除非指针设置正确,否则无法保证这种情况。指针指向的变量类型是最外面的星号。

int n1;
n1 = *p1;

无效的解除引用可能会导致崩溃,也可能不会导致崩溃:

  • 取消引用未初始化的指针可能会导致崩溃
  • 使用无效类型转换取消引用可能会导致崩溃。
  • 取消引用指向动态分配并随后取消分配的变量的指针可能会导致崩溃
  • 取消引用指向已超出范围的变量的指针也会导致崩溃。

无效引用更可能导致编译器错误而不是崩溃,但依赖编译器并不是一个好主意。

参考文献:

http://www.codingunit.com/cplusplus-tutorial-pointers-reference-and-dereference-operators

& is the reference operator and can be read as “address of”.
* is the dereference operator and can be read as “value pointed by”.

http://www.cplusplus.com/doc/tutorial/pointers/

& is the reference operator    
* is the dereference operator

http://en.wikipedia.org/wiki/Dereference_operator

The dereference operator * is also called the indirection operator.

16
投票

我总是听到他们使用的是相反的意义:

  • &是引用运算符 - 它为您提供了某个对象的引用(指针)
  • *是解引用运算符 - 它接受引用(指针)并返回引用的对象;

11
投票

首先,你有他们倒退:&是参考,*是解除引用。

引用变量意味着访问变量的内存地址:

int i = 5;
int * p;
p = &i; //&i returns the memory address of the variable i.

取消引用变量意味着访问存储在存储器地址的变量:

int i = 5;
int * p;
p = &i;
*p = 7; //*p returns the variable stored at the memory address stored in p, which is i.
//i is now 7

9
投票

找到以下解释:

int main()
{
    int a = 10;// say address of 'a' is 2000;
    int *p = &a; //it means 'p' is pointing[referencing] to 'a'. i.e p->2000
    int c = *p; //*p means dereferncing. it will give the content of the address pointed by 'p'. in this case 'p' is pointing to 2000[address of 'a' variable], content of 2000 is 10. so *p will give 10. 
}

结论:

  1. & [地址运算符]用于引用。
  2. * [星号运算符]用于取消引用。

3
投票

引用

&是参考运营商。它会将内存地址引用到指针变量。

Example:

int *p;
int a=5;
p=&a; // Here Pointer variable p refers to the address of integer variable a.

取消引用

指针变量使用解引用运算符*来直接访问变量的值而不是其内存地址。

Example:

int *p;
int a=5;
p=&a;
int value=*p; // Value variable will get the value of variable a that pointer variable p pointing to.

1
投票

*所处的上下文有时会混淆含义。

  // when declaring a function
int function(int*); // This function is being declared as a function that takes in an 'address' that holds a number (so int*), it's asking for a 'reference', interchangeably called 'address'. When I 'call'(use) this function later, I better give it a variable-address! So instead of var, or q, or w, or p, I give it the address of var so &var, or &q, or &w, or &p.   

//even though the symbol ' * ' is typically used to mean 'dereferenced variable'(meaning: to use the value at the address of a variable)--despite it's common use, in this case, the symbol means a 'reference', again, in THIS context. (context here being the declaration of a 'prototype'.) 


    //when calling a function
int main(){ 
    function(&var);  // we are giving the function a 'reference', we are giving it an 'address'
  }

因此,在声明诸如int或char之类的类型的上下文中,我们将使用dereferencer'*'来实际表示引用(地址),如果您看到编译器的错误消息说:'expecting',这会让您感到困惑char *'这是要求一个地址。

在这种情况下,当*在类型(int,char等)之后时,编译器期望变量的地址。我们通过使用引用运算符给出它,alos在变量之前称为运算符'&'的地址。更进一步,在我刚刚编写的情况下,编译器期望地址保存字符值,而不是数字。 (键入char * ==具有字符的值的地址)

int* p;
int *a;   // both are 'pointer' declarations. We are telling the compiler that we will soon give these variables an address (with &).

int c = 10;  //declare and initialize a random variable
//assign the variable to a pointer, we do this so that we can modify the value of c from a different function regardless of the scope of that function (elaboration in a second)

p = c; //ERROR, we assigned a 'value' to this 'pointer'. We need to assign an 'address', a 'reference'.
p = &c; // instead of a value such as: 'q',5,'t', or 2.1 we gave the pointer an 'address', which we could actually print with printf(), and would be something like
//so
p = 0xab33d111; //the address of c, (not specifically this value for the address, it'll look like this though, with the 0x in the beggining, the computer treats these different from regular numbers)
*p = 10; // the value of c

a = &c; // I can still give c another pointer, even though it already has the pointer variable "p"

*a = 10;
 a = 0xab33d111;

将每个变量视为具有位置(如果您熟悉数组,则为索引值)和值。可能需要一些时间来考虑每个变量具有两个值,一个值是它的位置,在计算机中物理存储电力,以及表示程序员想要存储的任何数量或字母的值。

//Why it's used
int function(b){
    b = b + 1; // we just want to add one to any variable that this function operates on.
} 

int main(){

    int c = 1;  // I want this variable to be 3.

    function(c); 
    function(c);// I call the function I made above twice, because I want c to be 3.

     // this will return c as 1. Even though I called it twice.
     // when you call a function it makes a copy of the variable.
     // so the function that I call "function", made a copy of c, and that function is only changing the "copy" of c, so it doesn't affect the original
}
  //let's redo this whole thing, and use pointers

int function(int* b){ // this time, the function is 'asking' (won't run without) for a variable that 'points' to a number-value (int). So it wants an integer pointer--an address that holds a number.
*b = *b + 1; //grab the value of the address, and add one to the value stored at that address
}

int main(){
    int c = 1; //again, I want this to be three at the end of the program
    int *p = &c; // on the left, I'm declaring a pointer, I'm telling the compiler that I'm about to have this letter point to an certain spot in my computer. Immediately after I used the assignment operator (the ' = ') to assign the address of c to this variable (pointer in this case) p. I do this using the address-of operator (referencer)' & '.
    function(p); // not *p, because that will dereference. which would give an integer, not an integer pointer ( function wants a reference to an int called int*, we aren't going to use *p because that will give the function an int instead of an address that stores an int.

    function(&c); // this is giving the same thing as above, p = the address of c, so we can pass the 'pointer' or we can pass the 'address' that the pointer(variable) is 'pointing','referencing' to. Which is &c. 0xaabbcc1122...


      //now, the function is making a copy of c's address, but it doesn't matter if it's a copy or not, because it's going to point the computer to the exact same spot (hence, The Address), and it will be changed for main's version of c as well.

}

在每个块内,它复制传入的变量(如果有的话)(通过“()”中的参数)。在这些块中,对变量的更改是对该变量的副本进行的,该变量使用相同的字母但位于不同的地址(与原始地址不同)。通过使用原始地址“reference”,我们可以使用main之外的块或main的子级内部来更改变量。

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