填充问题？(C/GCC)

Question

我试图统一一个ARM项目(特别是运行Linux 2.6.33.3的i.MX27 CPU,用GCC 4.3.2编译)的SQLite交互方法.作为其中的一部分,我创建了一个带有union的结构,该结构用于保存绑定到预准备语句的值.

#define SQLITE_DATA_CHARACTER_STRING_MAX 1024

typedef struct
{
    int data_type;
    union
    {
        int integer;
        double floating_point;
        unsigned char character_string[SQLITE_DATA_CHARACTER_STRING_MAX];
    };
}sqlite_data;

原来,这是int,float,char.我想用long long,double和char.但是,这似乎导致了一个问题.如上所述,以下代码生成可预测的输出:

int data_fields = 15;
int data_fields_index = 0;
sqlite_data data[data_fields];

LogMsg(LOG_INFO, "%s: Assigning", __FUNCTION__);

for(data_fields_index = 0; data_fields_index < data_fields; data_fields_index++)
{
    data[data_fields_index].data_type = (100 + data_fields_index);
    data[data_fields_index].integer = (1000 + data_fields_index);
    LogMsg(LOG_INFO, "%s: data[%d] - %d; type - %d", __FUNCTION__, data_fields_index, data[data_fields_index].integer, data[data_fields_index].data_type);
}

其输出是这样的:

 Assigning
 data[0] - 1000; type - 100
 data[1] - 1001; type - 101
 data[2] - 1002; type - 102
 data[3] - 1003; type - 103
 data[4] - 1004; type - 104
 data[5] - 1005; type - 105
 data[6] - 1006; type - 106
 data[7] - 1007; type - 107
 data[8] - 1008; type - 108
 data[9] - 1009; type - 109
 data[10] - 1010; type - 110
 data[11] - 1011; type - 111
 data[12] - 1012; type - 112
 data[13] - 1013; type - 113
 data[14] - 1014; type - 114

但是,如果我只进行一次更改(给出integer类型long long),它就会崩溃.那么,以下变化:

typedef struct
{
    int data_type;
    union
    {
        long long integer;
        double floating_point;
        unsigned char character_string[SQLITE_DATA_CHARACTER_STRING_MAX];
    };
}sqlite_data;

生成此输出:

Assigning
data[0] - 1000; type - 0
data[1] - 1001; type - 0
data[2] - 1002; type - 0
data[3] - 1003; type - 0
data[4] - 1004; type - 0
data[5] - 1005; type - 0
data[6] - 1006; type - 0
data[7] - 1007; type - 0
data[8] - 1008; type - 0
data[9] - 1009; type - 0
data[10] - 1010; type - 0
data[11] - 1011; type - 0
data[12] - 1012; type - 0
data[13] - 1013; type - 0
data[14] - 1014; type - 0

我已经尝试将它们去实现它们,使用#pragma pack(6)并将该数组放在堆上,所有这些都具有相同的结果:int工作,long long但不是.

这里发生了什么？

Answer 1

你没有告诉printf()期待long long.使用%lld您的格式字符串代替%d.