C 指针学习

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指针词库：

type *ptr

type类型的指针，名为ptr。

*ptrc

ptr所指向位置的值。

*(ptr + i)

（ptr所指向位置加上i）的值。以字节为单位的话，应该是ptr所指向的位置再加上sizeof(type) * i。

&thing

thing的地址。

type *ptr = &thing

名为ptr，type类型的指针，值设置为thing的地址。

ptr++

自增ptr指向的位置。

代码演练：

#include 
int main(int argc, char *argv[])
{
    // create two arrays we care about
    int ages[] = {23, 43, 12, 89, 2};
    char *names[] = {"Alan", "Frank","Mary", "John", "Lisa"};
    // safely get the size of ages
    int count = sizeof(ages) / sizeof(int);
    int i = 0;
    // first way using indexing
    for(i = 0; i < count; i++) {
        printf("%s has %d years alive.\n",
                names[i], ages[i]);
    }
    printf("---\n");
    // setup the pointers to the start of the arrays
    int *cur_age = ages;
    char **cur_name = names;
    // second way using pointers
    for(i = 0; i < count; i++) {
        printf("%s is %d years old.\n",
                *(cur_name+i), *(cur_age+i));
    }
    printf("---\n");
    // third way, pointers are just arrays
    for(i = 0; i < count; i++) {
        printf("%s is %d years old again.\n",
                cur_name[i], cur_age[i]);
    }
    printf("---\n");
    // fourth way with pointers in a stupid complex way
    for(cur_name = names, cur_age = ages;
            (cur_age - ages) < count;
            cur_name++, cur_age++)
    {
        printf("%s lived %d years so far.\n",
                *cur_name, *cur_age);
    }
    return 0;
}

运行结果：

Alan has 23 years alive.
Frank has 43 years alive.
Mary has 12 years alive.
John has 89 years alive.
Lisa has 2 years alive.
---
Alan is 23 years old.
Frank is 43 years old.
Mary is 12 years old.
John is 89 years old.
Lisa is 2 years old.
---
Alan is 23 years old again.
Frank is 43 years old again.
Mary is 12 years old again.
John is 89 years old again.
Lisa is 2 years old again.
---
Alan lived 23 years so far.
Frank lived 43 years so far.
Mary lived 12 years so far.
John lived 89 years so far.
Lisa lived 2 years so far.