C语言中的增量后和增量前

我对这两个C语句有一个问题：

x=y++

t=*ptr++

对于语句1，y的初始值被复制到x中，然后y递增

在语句2中，我们查看*ptr指向的值，将其放入变量t中，然后在稍后增加ptr

对于语句1，后缀增量运算符的优先级高于赋值运算符。那么，y不应该先递增，然后将x分配给y的递增值吗

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在这些情况下，我不理解运算符优先级。

您对

2]

的含义理解错误。增量后总是产生增量之前的值，然后在增量后的某个时间增加该值

因此，

t=*ptr++

本质上等同于：

t = *ptr;
ptr = ptr + 1;

这同样适用于您的

1]

——从

y++

生成的值是增量之前的

y

的值。优先级不会改变这一点——不管表达式中其他运算符的优先级有多高或多低，它产生的值始终是增量之前的值，增量将在之后某个时间进行。

C中增量前和增量后的差异： 增量前和增量后是内置的。一元的意思是：“有一个输入的函数”。“运算符”表示：“对变量进行修改”

增量（++）和减量（-）内置一元运算符修改它们附加到的变量。如果试图对常量或文字使用这些一元运算符，则会出现错误

在C中，以下是所有内置一元运算符的列表：

Increment:         ++x, x++
Decrement:         −−x, x−−
Address:           &x
Indirection:       *x
Positive:          +x
Negative:          −x
Ones_complement:  ~x
Logical_negation:  !x
Sizeof:            sizeof x, sizeof(type-name)
Cast:              (type-name) cast-expression

这些内置运算符是伪装的函数，它们接受变量输入并将计算结果放回同一变量中

后增量示例：

int x = 0;     //variable x receives the value 0.
int y = 5;     //variable y receives the value 5

x = y++;       //variable x receives the value of y which is 5, then y 
               //is incremented to 6.

//Now x has the value 5 and y has the value 6.
//the ++ to the right of the variable means do the increment after the statement

int x = 0;     //variable x receives the value 0.
int y = 5;     //variable y receives the value 5

x = ++y;       //variable y is incremented to 6, then variable x receives 
               //the value of y which is 6.

//Now x has the value 6 and y has the value 6.
//the ++ to the left of the variable means do the increment before the statement

int x = 0;     //variable x receives the value 0.
int y = 5;     //variable y receives the value 5

x = y--;       //variable x receives the value of y which is 5, then y 
               //is decremented to 4.

//Now x has the value 5 and y has the value 4.
//the -- to the right of the variable means do the decrement after the statement

int x = 0;     //variable x receives the value 0.
int y = 5;     //variable y receives the value 5

x = --y;       //variable y is decremented to 4, then variable x receives 
               //the value of y which is 4.

//x has the value 4 and y has the value 4.
//the -- to the right of the variable means do the decrement before the statement

预增量示例：

int x = 0;     //variable x receives the value 0.
int y = 5;     //variable y receives the value 5

x = y++;       //variable x receives the value of y which is 5, then y 
               //is incremented to 6.

//Now x has the value 5 and y has the value 6.
//the ++ to the right of the variable means do the increment after the statement

int x = 0;     //variable x receives the value 0.
int y = 5;     //variable y receives the value 5

x = ++y;       //variable y is incremented to 6, then variable x receives 
               //the value of y which is 6.

//Now x has the value 6 and y has the value 6.
//the ++ to the left of the variable means do the increment before the statement

int x = 0;     //variable x receives the value 0.
int y = 5;     //variable y receives the value 5

x = y--;       //variable x receives the value of y which is 5, then y 
               //is decremented to 4.

//Now x has the value 5 and y has the value 4.
//the -- to the right of the variable means do the decrement after the statement

int x = 0;     //variable x receives the value 0.
int y = 5;     //variable y receives the value 5

x = --y;       //variable y is decremented to 4, then variable x receives 
               //the value of y which is 4.

//x has the value 4 and y has the value 4.
//the -- to the right of the variable means do the decrement before the statement

后减量示例：

int x = 0;     //variable x receives the value 0.
int y = 5;     //variable y receives the value 5

x = y++;       //variable x receives the value of y which is 5, then y 
               //is incremented to 6.

//Now x has the value 5 and y has the value 6.
//the ++ to the right of the variable means do the increment after the statement

int x = 0;     //variable x receives the value 0.
int y = 5;     //variable y receives the value 5

x = ++y;       //variable y is incremented to 6, then variable x receives 
               //the value of y which is 6.

//Now x has the value 6 and y has the value 6.
//the ++ to the left of the variable means do the increment before the statement

int x = 0;     //variable x receives the value 0.
int y = 5;     //variable y receives the value 5

x = y--;       //variable x receives the value of y which is 5, then y 
               //is decremented to 4.

//Now x has the value 5 and y has the value 4.
//the -- to the right of the variable means do the decrement after the statement

int x = 0;     //variable x receives the value 0.
int y = 5;     //variable y receives the value 5

x = --y;       //variable y is decremented to 4, then variable x receives 
               //the value of y which is 4.

//x has the value 4 and y has the value 4.
//the -- to the right of the variable means do the decrement before the statement

预减量示例：

int x = 0;     //variable x receives the value 0.
int y = 5;     //variable y receives the value 5

x = y++;       //variable x receives the value of y which is 5, then y 
               //is incremented to 6.

//Now x has the value 5 and y has the value 6.
//the ++ to the right of the variable means do the increment after the statement

int x = 0;     //variable x receives the value 0.
int y = 5;     //variable y receives the value 5

x = ++y;       //variable y is incremented to 6, then variable x receives 
               //the value of y which is 6.

//Now x has the value 6 and y has the value 6.
//the ++ to the left of the variable means do the increment before the statement

int x = 0;     //variable x receives the value 0.
int y = 5;     //variable y receives the value 5

x = y--;       //variable x receives the value of y which is 5, then y 
               //is decremented to 4.

//Now x has the value 5 and y has the value 4.
//the -- to the right of the variable means do the decrement after the statement

int x = 0;     //variable x receives the value 0.
int y = 5;     //variable y receives the value 5

x = --y;       //variable y is decremented to 4, then variable x receives 
               //the value of y which is 4.

//x has the value 4 and y has the value 4.
//the -- to the right of the variable means do the decrement before the statement

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如果这让你感到困惑，你可能会想读一读，把它说出来。正如我所说，指针首先递增。检查以下内容：“后缀++运算符的结果是操作数的值。获得结果后，操作数的值将递增。”（来自C99标准的§6.5.2.4/2）。您是正确的。我想我可以相信c-faq，遵循标准it是最好的策略。道歉。@Pkp：我认为你误解了常见问题。这里要解决的问题是

++

是否将应用于指针本身，或者指针所指的内容（顺便说一句，这也是优先级在本例中确定的内容）。答案是它适用于指针本身，而不是指针对象。