Sequence of operations when using pointers and auto-incrementing operators in C Language

Sequence of operations when using pointers and auto-incrementing operators in C Language

In the C language, when the pointer operator and ++ or-are combined, it is easy to tell the unclear operation order. Here, we will summarize the following six combinations: * p ++, (* p) ++, * (p ++), ++ * p, ++ (* p), * (++ p ).

First look at the code and output:

#include
  
   int main(){    int a[3]={1,3,5};    int *p=a;    printf(----------------1----------------);    printf(%d,*p++);    printf(%d,*p);    int i;    for(i=0;i<3;i++)        printf(%d ,a[i]);    printf();    printf(----------------2----------------);    p=a;//reset data    printf(%d,(*p)++);    printf(%d,*p);    for(i=0;i<3;i++)        printf(%d ,a[i]);    printf();    printf(----------------3----------------);    a[0]=1;//reset data    p=a;    printf(%d,*(p++));    printf(%d,*p);    for(i=0;i<3;i++)        printf(%d ,a[i]);    printf();    printf(----------------4----------------);    p=a;    printf(%d,++*p);    printf(%d,*p);    for(i=0;i<3;i++)        printf(%d ,a[i]);    printf();    printf(----------------5----------------);    p=a;    a[0]=1;    printf(%d,++(*p));    printf(%d,*p);    for(i=0;i<3;i++)        printf(%d ,a[i]);    printf();    printf(----------------6----------------);    p=a;    a[0]=1;    printf(%d,*(++p));    printf(%d,*p);    for(i=0;i<3;i++)        printf(%d ,a[i]);    printf();    return 0;}
  

The output result is as follows:

First group: * p ++. The operation sequence is to first return the value of * p, and then p ++.
The second group: (* p) ++. the operation order is to first return the value of * p, then the value of * p Plus ++, this can be seen from the value of array a after calculation.
Group 3: * (p ++). the operation order is to first return the value of * p, and then p ++, that is, it is the same as the operation order of * p ++.

All three groups return the value of * p first. The difference is whether the value of * p is p ++ or * p ++.

Group 4: + + * p. Set the value of * p to + +, and then return the value of * p.
Group 5: ++ (* p), first convert the value of * p to ++, and then return the value of * p, so it is the same as ++ * p.
Group 6: * (++ p). First, the value of p is ++, and then the value of * p is returned, which is equivalent to * ++ p.

These three groups are characterized by * p values returned at the end, with the difference being * p ++ or p ++.