c - C中“引用”和“取消引用”的含义
* 所在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int 或 char 等类型的上下文中，我们将使用解引用器 ' * ' 来实际表示引用（地址），如果您看到来自编译器的错误消息说：'expecting char*' 要求地址。
在这种情况下，当 * 位于类型（int、char 等）之后时，编译器会期望变量的地址。我们通过使用引用运算符来赋予它，在变量之前也称为地址运算符'&'。更进一步，在我刚才编造的情况下，编译器期望地址保存一个字符值，而不是一个数字。（类型 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习惯认为每个变量都有两个值，一个值是它的位置，与计算机中的电力一起物理存储，另一个值代表程序员想要存储的任何数量或字母。
//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.
}
在每个块中，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“引用”，我们可以使用 main 之外的块或 main 的子项内部的块来更改变量。