Linux GNU C结构体数组初始化示例

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实然心血来潮，想学习一下结构体数组的初始化方面的知识。

以下是GCC实然心血来潮，想学习一下结构体数组的初始化方面的知识。特有的数组初始化的风格：

// 数组赋值另一种方式，但只在gcc下编译通过，g++不能enum {    AAA = 0,BBB,CCC,DDD,};// 只对感兴趣的索引值进行赋值，而不管下标的顺序static const int regs[] = {    [DDD] = 250,    [CCC] = 3,    [AAA] = 180,};

这种风格在kernel代码中经常看到。它不按照数组下标顺序，而是使用自定义的“索引”来赋值，比如Intel网卡igb驱动中一处代码：

static const struct e1000_info *igb_info_tbl[] = {[board_82575] = &e1000_82575_info,};

从代码中可以清晰知道，这个结构体是针对82575的——board_82575比数字0更直观易读。

但是使用g++却无法编译，编译错误提示如下：

sorry, unimplemented: non-trivial designated initializers not supported

下面再看看结构体数组的初始化，先给出结构体的定义：

enum control_type{    TYPE_GPIO = 0,    TYPE_IIC = 1,    TYPE_SPI = 2,};typedef struct control_info_t {    const char*name;    enum control_type type;    int enable;}control_info;

初始化方式一，依次给数组内元素赋值，如下：：

control_info control_info1[3] =     {        {"FOO_GPIO", TYPE_GPIO, 1},        {"FOO_IIC", TYPE_IIC, 0},        {"FOO_SPI", TYPE_SPI, 1},    };

方式二，先声明再赋值，如下：

control_info control_info[3];    control_info[TYPE_SPI].name = "FOO_SPI";    control_info[TYPE_SPI].type = TYPE_SPI;    control_info[TYPE_SPI].enable = 1;

方式三，不按照顺序，只对感兴趣几项赋值，如下：

control_info control_info2[3] =     {        [TYPE_SPI] = {"FOO_SPI", TYPE_SPI, 1},        [TYPE_GPIO] = {"FOO_GPIO", TYPE_GPIO, 1},    };

从这个方式上看，类型为SPI的“索引值”对应即为SPI，但无须理会类型SPI的具体值。

本文完整代码如下：

/**结果：struct test250 0 180 3111 name: FOO_IIC type: 1 enable: 0222 name: FOO_GPIO type: 0 enable: 1333 name: FOO_SPI type: 2 enable: 1*/#include <stdio.h>#include <inttypes.h>///////////////////////// 简单int类型的数组// 数组赋值另一种方式，但只在gcc下编译通过，g++不能enum {    AAA = 0,BBB,CCC,DDD,};// 只对感兴趣的索引值进行赋值，而不管下标的顺序static const int regs[] = {    [DDD] = 250,    [CCC] = 3,    [AAA] = 180,};void struct_test1(){    printf("%d %d %d %d\n", regs[DDD], regs[BBB], regs[AAA], regs[CCC]);}///////////////////////// 结构体数组初始化示例enum control_type{    TYPE_GPIO = 0,    TYPE_IIC = 1,    TYPE_SPI = 2,};typedef struct control_info_t {    const char*name;    enum control_type type;    int enable;}control_info;void struct_test_2(){    // c++风格，用g++并使用 -std=c++11    //control_info gcontrol_info0 {.name = "FOO", .type = TYPE_SPI, .enable=1};    // 三个依次赋值    control_info control_info1[3] =     {        {"FOO_GPIO", TYPE_GPIO, 1},        {"FOO_IIC", TYPE_IIC, 0},        {"FOO_SPI", TYPE_SPI, 1},    };    printf("111 name: %s type: %d enable: %d\n", control_info1[TYPE_IIC].name, control_info1[TYPE_IIC].type, control_info1[TYPE_IIC].enable);        // GNU风格赋值    control_info control_info2[3] =     {        [TYPE_SPI] = {"FOO_SPI", TYPE_SPI, 1},        [TYPE_GPIO] = {"FOO_GPIO", TYPE_GPIO, 1},    };    printf("222 name: %s type: %d enable: %d\n", control_info2[TYPE_GPIO].name, control_info2[TYPE_GPIO].type, control_info2[TYPE_GPIO].enable);            // 只有一个赋值    control_info control_info[3];    control_info[TYPE_SPI].name = "FOO_SPI";    control_info[TYPE_SPI].type = TYPE_SPI;    control_info[TYPE_SPI].enable = 1;        printf("333 name: %s type: %d enable: %d\n", control_info[TYPE_SPI].name, control_info[TYPE_SPI].type, control_info[TYPE_SPI].enable);}int main(void){    printf("struct test\n");    struct_test1();    struct_test_2();        return 0;}

李迟 2016.10.13 周四中午午休前

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