结构体中指针

结构体中带有指针的情况

#include<stdio.h>

struct man
{
    char *name;
    int age;
};

int main()
{
    struct man m = {"tom",20};
    printf("name = %s, age = %d
",m.name,m.age);
    return 0;
}

运行结果：

exbot@ubuntu:~/wangqinghe/C/20190714$ gcc struct.c -o struct

exbot@ubuntu:~/wangqinghe/C/20190714$ ./struct

name = tom, age = 20

如果修改m.name的值

#include<stdio.h>
#include<string.h>

struct man
{
    char *name;
    int age;
};

int main()
{
    struct man m = {"tom",20};
    strcpy(m.name,"mike");
    printf("name = %s, age = %d
",m.name,m.age);
    return 0;
}

exbot@ubuntu:~/wangqinghe/C/20190714$ gcc struct.c -o struct

exbot@ubuntu:~/wangqinghe/C/20190714$ ./struct

段错误 (核心已转储)

会出现以上错误。

将指针改位数组：

#include<stdio.h>
#include<string.h>

struct man
{
    char name[256];
    int age;
};

int main()
{
    struct man m = {"tom",20};
    strcpy(m.name,"mike");
    printf("name = %s, age = %d
",m.name,m.age);
    return 0;
}

编译运行：

exbot@ubuntu:~/wangqinghe/C/20190714$ gcc struct.c -o struct

exbot@ubuntu:~/wangqinghe/C/20190714$ ./struct

name = mike, age = 20

分析：

常量内存中的数值是不能修改的。

#include<stdio.h>
#include<string.h>
#include<stdlib.h>

struct man
{
    char *name;
    int age;
};

int main()
{
    //struct man m = {"tom",20};
    struct man m;
    m.name = malloc(sizeof(char) * 100);
    m.age = 20;
    strcpy(m.name,"mike");
    printf("name = %s, age = %d
",m.name,m.age);
    return 0;
}

编译运行：

exbot@ubuntu:~/wangqinghe/C/20190714$ gcc struct.c -o struct

exbot@ubuntu:~/wangqinghe/C/20190714$ ./struct

name = mike, age = 20

#include<stdio.h>
#include<string.h>
#include<stdlib.h>

struct man
{
    char *name;
    int age;
};

int main()
{
    struct man *p = malloc(sizeof(struct man));
    p->name = malloc(sizeof(char) * 100);
    strcpy(p->name,"tom");
    p->age = 30;
    printf("name = %s, age = %d
",p->name,p->age);
    free(p->name);
    free(p);
    return 0;
}

指针在内存的存储方式：

exbot@ubuntu:~/wangqinghe/C/20190714$ gcc struct.c -o struct

exbot@ubuntu:~/wangqinghe/C/20190714$ ./struct

name = tom, age = 30

END