如何自动为结构中的字节添加填充以修复 C 中的寄存器对齐？

C11 允许对齐控制。

也许让许多成员结盟 - 任何时候，限制性更强的成员都可能跟随限制性较小的成员。

#include <stdalign.h>

struct configStruct {
    char description[32];
    alignas (short) float c1CE_A; // coefficient 1_A
    float c1CE_B; // coefficient 1_B
    float c1CE_C; // coefficient 1_C
    char c1useLogFit;
    alignas (short) float c2CE_A;
    float c2CE_B;
    float c2CE_C;
    char cc2useLogFit;
    alignas (short) float c3CE_A;
    float c3CE_B;
    float c3CE_C;
    char c3useLogFit;
    char dummyByte;
};

大多数编译器将填充添加到 a 中以达到对齐目的。假设 a 为 4 个字节，则结构的实际布局如下所示：structfloat

struct configStruct { 
    char description[32];
    float c1CE_A; 
    float c1CE_B; 
    float c1CE_C; 
    char c1useLogFit; 
    char dummy[3];    // padding bytes
    float c2CE_A;
    float c2CE_B;
    float c2CE_C;
    char c2useLogFit;
    char dummy[3];    // padding bytes
    float c3CE_A;
    float c3CE_B;
    float c3CE_C;
    char c3useLogFit;
    char dummyByte;
    char dummy[2];    // padding bytes
};

所以你的 72 字节结构实际上是 80 字节。

如果你使用的是 gcc，你可以声明要打包的结构体：

struct configStruct __attribute__((packed)) { 
    char description[32];
    float c1CE_A; 
    float c1CE_B; 
    float c1CE_C; 
    char c1useLogFit; 
    float c2CE_A;
    float c2CE_B;
    float c2CE_C;
    char c2useLogFit;
    float c3CE_A;
    float c3CE_B;
    float c3CE_C;
    char c3useLogFit;
    char dummyByte;
};

这将消除填充。

如果没有，则需要手动反序列化数据以处理它，因为它将序列化回字节缓冲区以将其写入另一端。

如何执行此操作的示例如下：

void deserialize(char *indata, struct configStruct *data)
{
    char *p = indata;
    int offset = 0;
    memcpy(data->description, p + offset, sizeof(data->description));
    offset += sizeof(data->description);
    memcpy(&data->c1CE_A, p + offset, sizeof(data->c1CE_A));
    offset += sizeof(data->c1CE_A);
    memcpy(&data->c1CE_B, p + offset, sizeof(data->c1CE_B));
    offset += sizeof(data->c1CE_B);
    memcpy(&data->c1CE_C, p + offset, sizeof(data->c1CE_C));
    offset += sizeof(data->c1CE_C);
    memcpy(&data->c1useLogFit, p + offset, sizeof(data->c1useLogFit));
    offset += sizeof(data->c1useLogFit);
    // etc.
}

void serialize(struct configStruct *data, char *outdata)
{
    char *p = outdata;
    int offset = 0;
    memcpy(p + offset, data->description, sizeof(data->description));
    offset += sizeof(data->description);
    memcpy(p + offset, &data->c1CE_A, sizeof(data->c1CE_A));
    offset += sizeof(data->c1CE_A);
    memcpy(p + offset, &data->c1CE_B, sizeof(data->c1CE_B));
    offset += sizeof(data->c1CE_B);
    memcpy(p + offset, &data->c1CE_C, sizeof(data->c1CE_C));
    offset += sizeof(data->c1CE_C);
    memcpy(p + offset, &data->c1useLogFit, sizeof(data->c1useLogFit));
    offset += sizeof(data->c1useLogFit);
    // etc.
}

int MacroEntry()
{

    char indata[72], outdata[72];
    struct configStruct data;

    ReadData(ProductConfig_PLC,1,2305,36,(void*)indata); 
    deserialize(indata, &data);

    // work with "data"

    serialize(&data, outdata);
    WriteData(ProductConfig_HMI,0,2305,36,(void*)outdata); // write temporary data to HMI from struct

    return 0;
}