如何重新排序整数的字节？ [英] How can I reorder the bytes of an integer?

问题描述

我的任务是将数据文件从大端转换为小端&反之亦然。使用C。相反，我已经在网上寻找了大约3个小时的其他示例并阅读了我的教科书，但是，我对如何启动此功能一无所知。

My task is to convert a data file from big endian to little endian & vice versa using C. I have been looking online for about 3 hours now for other examples and reading my text book, however I am so stuck on how to even start this function.

到目前为止，我的事件顺序是正确的（1到4），但是在我的 convert_and_save 函数内部，我必须使用→创建一个char数组。 char buffer [4]; ？

So far I have the order of events correct (1 through 4) but inside my convert_and_save function do I have to create a char array using → char buffer[4];?

有人可以帮助我吗？即使您只是提供有关查找内容的线索，我也将不胜感激。

Can someone please help me? even if you just give me clues on what to look up, I would greatly appreciate it.

我需要编写一个函数：

void convert_and_save(struct record item, FILE * output_handle, int number);

在此功能内，我执行以下一系列步骤：

inside this function I do the following series of steps:

1. 使用以下方法将整数转换为字符数组：

1. Convert the integer into an array of chars using:

int integer_to_characters(int number, char * buffer)
{
   memcpy(buffer, &number, 4);
}

反转该数组中字符的顺序。

Reverse the order of the chars in that array.

使用以下方式将字符数组转换回整数：

Convert the array of chars back to an integer using:

int characters_to_integer(char * buffer)
{
   int result;
   memcpy(&result, buffer, 4);
   return result;
}

使用以下命令将转换后的记录写入输出文件：

write the converted record on the output file using:

void save_record(FILE * file_handle, struct record a)
{
   char output_buffer[size_of_record];
   integer_to_characters(a.age, &(output_buffer[0]));
   memcpy(&(output_buffer[4]), a.name, 12);
   integer_to_characters(a.department, &(output_buffer[16]));
   fwrite(output_buffer, sizeof(char), size_of_record, file_handle);
}

推荐答案

这些不是标准功能（这些是gcc扩展名），但是您可以使用它们：

These are not standard function (these are gcc extensions), but you may be able to use them:

内置函数：uint16_t __builtin_bswap16（uint16_t x）返回x
，其字节顺序相反；例如，0xaabb变为
0xbbaa。字节在这里始终意味着恰好是8位。

— Built-in Function: uint16_t __builtin_bswap16 (uint16_t x) Returns x with the order of the bytes reversed; for example, 0xaabb becomes 0xbbaa. Byte here always means exactly 8 bits.

—内置函数：uint32_t __builtin_bswap32（uint32_t x）与__builtin_bswap16类似的
，除了参数和返回类型是

— Built-in Function: uint32_t __builtin_bswap32 (uint32_t x) Similar to __builtin_bswap16, except the argument and return types are 32 bit.

—内置函数：uint64_t __builtin_bswap64（uint64_t x）与__builtin_bswap32类似的
，只是参数和返回类型为64位。 p>

— Built-in Function: uint64_t __builtin_bswap64 (uint64_t x) Similar to __builtin_bswap32, except the argument and return types are 64 bit.

如果可以使用它们，很可能会为您的平台带来更优化的代码，否则，请提交补丁到gcc：）

If you can use these, chances are it will result in more optimal code for your platform, if not, good job, submit a patch to gcc :)

Clang也有 __ builtin_bswap16（）__builtin_bswap32（）__builtin_bswap64（）

Visual Studio

Visual Studio

unsigned short _byteswap_ushort (
   unsigned short val
);
unsigned long _byteswap_ulong (
   unsigned long val
);
unsigned __int64 _byteswap_uint64 (
   unsigned __int64 val
);

ICC具有 _bswap16，_bswap和_bswap64 *需要更多参考

ICC has _bswap16, _bswap and _bswap64 *need further reference

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