Linux GNU C结构体数组初始化示例

突然心血来潮，想学习一下结构体数组的初始化方面的知识。

GCC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 test
250 0 180 3
111 name: FOO_IIC type: 1 enable: 0
222 name: FOO_GPIO type: 0 enable: 1
333 name: FOO_SPI type: 2 enable: 1
*/

#include 
#include 

///////////////////////
// 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