内核代码中一些c语言用法

container_of，（C 语言 up cast） 

内核中的定义：

Cscope tag: container_of
   #   line  filename / context / line
   1     27  drivers/gpu/drm/radeon/mkregtable.c <<container_of>>
             #define container_of(ptr, type, member) ({
   2     63  drivers/staging/lustre/include/linux/libcfs/libcfs.h <<container_of>>
             #define container_of(ptr, type, member)
   3     78  drivers/staging/rtl8192e/rtllib.h <<container_of>>
             #define container_of(ptr, type, member) ({
   4     61  drivers/staging/rtl8192u/ieee80211/ieee80211.h <<container_of>>
             #define container_of(ptr, type, member) ({
   5    791  include/linux/kernel.h <<container_of>>
             #define container_of(ptr, type, member) ({
   6     18  scripts/kconfig/list.h <<container_of>>
             #define container_of(ptr, type, member) ({
   7     26  tools/perf/util/include/linux/kernel.h <<container_of>>
             #define container_of(ptr, type, member) ({
   8     84  tools/virtio/linux/kernel.h <<container_of>>
             #define container_of(ptr, type, member) ({

scripts/kconfig/list.h

#define offsetof(TYPE, MEMBER) ((size_t) &((TYPE *)0)->MEMBER)

/**
 * container_of - cast a member of a structure out to the containing structure
 * @ptr:        the pointer to the member.
 * @type:       the type of the container struct this is embedded in.
 * @member:     the name of the member within the struct.
 *
 */
#define container_of(ptr, type, member) ({                      
        const typeof( ((type *)0)->member ) *__mptr = (ptr);    
        (type *)( (char *)__mptr - offsetof(type,member) );})

分析详见：

http://www.cnblogs.com/cute/archive/2011/04/01/2002474.html

结构体和数据 

谈结构体struct 初始化多出的点号“.”，数组[]初始化多出的逗号“,”

cat test.c

内容如下：

#include <stdio.h>

#define MAXTITL 30
#define MAXAUTL 20

struct book {
  float off;
  char title[MAXTITL];
  char author[MAXAUTL];
  float value;

};

int main()
{
    puts("C lange test!");
    struct book b1 = { .value =  19.9, .author = "author", .title="C test tutorial" };
    printf("Book value: %f
", b1.value);
    printf("Book author: %s
", b1.author);
    printf("Book title: %s
", b1.title);
    printf("Book off: %f
", b1.off);
    int m,n;
    int a2[10] = {1, 2, 3, 4, 5, 6, 7, 8, 9, 0};
    for(n=0;n<11;n++)
        printf("%d
",a2[n]);
    int a1[10] = {1, 2, 3, 4, 5, 6, 7, 8, 9, 0, };
    for(m=0;m<11;m++)
        printf("%d
",a1[m]);
    return 0;
}

执行：

gcc test.c -o test
./test

　　

 

结构体的空数组

example 1， 求大小

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

struct tag1
{
      int a;
      int b;
}__attribute ((packed));   //size = 8

struct tag2
{
      int a;
      int b;
      char *c;
}__attribute ((packed));  //size = 12 on 32bit platform, 16 size on 64bit

struct tag3
{
    int a;
    int b;
    char c[0];
}__attribute ((packed));  //size = 8

struct tag4
{
    int a;
    int b;
    char c[1];
}__attribute ((packed));  //size = 9

int main()
{
      struct tag2 l_tag2;
      struct tag3 l_tag3;
      struct tag4 l_tag4;

      memset(&l_tag2,0,sizeof(struct tag2));
      memset(&l_tag3,0,sizeof(struct tag3));
      memset(&l_tag4,0,sizeof(struct tag4));

      printf("size of tag1 = %ld
",sizeof(struct tag1));
      printf("size of tag2 = %ld
",sizeof(struct tag2));
      printf("size of tag3 = %ld
",sizeof(struct tag3));
      printf("size of tag4 = %ld
",sizeof(struct tag4));

      printf("l_tag2 = %p,&l_tag2.c = %p,l_tag2.c = %p
",&l_tag2,&l_tag2.c,l_tag2.c);
      printf("l_tag3 = %p,l_tag3.c = %p
",&l_tag3,l_tag3.c);
      printf("l_tag4 = %p,l_tag4.c = %p
",&l_tag4,l_tag4.c);
      return 0;
}

example 2，柔性数组，动态内存

C语言0长度数组使用技巧， 又解决了小内存碎片问题提高了性能。

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

typedef struct{
    int stuID;
    int age;
    char address[];  // same with address[0]
}ST_STU_INFO,*pStuInfo; // size is 8

pStuInfo ComposeStuInfo( int stuID,int age, const char *paddress)
{
    pStuInfo ptmpInfo = malloc(sizeof(*ptmpInfo) + sizeof(char) * strlen(paddress) + 1);
    if(ptmpInfo != NULL){
        ptmpInfo->stuID = stuID;
        ptmpInfo->age = age;
        strcpy(ptmpInfo->address, paddress);
    }
    return ptmpInfo;
}

void printStuInfo(pStuInfo ptmpInfo)
{
    printf("stuID : %d, age : %d, 
Address: %s
"
           "Size of Struct：%ld

",
           ptmpInfo->stuID, ptmpInfo->age,
           ptmpInfo->address, sizeof(*ptmpInfo));
}

int main()
{
    pStuInfo CodeLab = ComposeStuInfo(
        100013, 20, "Tencent Building, Central District, High-tech Park, "
        "Nanshan District, Shenzhen");
    if(CodeLab != NULL){
        printStuInfo(CodeLab);
        free(CodeLab);
    }
    pStuInfo subCodeLab = ComposeStuInfo(200013, 23, "Tencent Building");
    if(subCodeLab != NULL){
        printStuInfo(subCodeLab);
        free(subCodeLab);
    }
    return 0;
}

c语言中__attribute__的意义

REF:

gcc 编译  

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[翻译]15个最常用的GCC编译器参数  

GCC编译优化指南  

GCC编译C语言程序完整演示   

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