作者：朱金灿
来源：clever101的专栏

  最近面临这样一个需求：以比较节省存储空间的存储一组坐标点到文件，要求程序能够跨平台读写这种文件。思考了一下，比较简单的方式是以二进制文件的方式保存，先存入点的个数，然后把点结构体逐个存储进去。因为要节省存储空间，得保证结构体是以单字节对齐的。代码如下：

#include <stdio.h>
#include <string>
#include <vector>


/* 对齐结构成员到1字节 */
#ifdef __GNUC__
#define GNUC_PACKED __attribute__((packed))
#else
#define GNUC_PACKED
#endif
#ifdef __arm 
#define ARM_PACKED  __packed 
#else 
#define ARM_PACKED 
#endif
#if defined(_WIN32) || defined(_WIN64)
#pragma pack(1)
#endif
ARM_PACKED

/*
坐标点结构体
*/
struct  stPointCoodinate
{
	double m_CoodinateX;  //x坐标
	double m_CoodinateY;  //y坐标
};

#if defined(_WIN32) || defined(_WIN64)
#pragma pack()
#endif

/*
将点结构体转化为二进制文件
具体是先写入点的数目，然后再逐个写入点
*/
int WritePointsToFile(const std::vector<stPointCoodinate>& vecTarget, const std::string& binFile)
{
	if (vecTarget.empty())
	{
		printf("point number is 0\n");
		return -1;
	}

	FILE* fp = fopen(binFile.c_str(), "wb");
	if (NULL == fp)
	{
		printf("create point file failed!\n");
		return -2;
	}
	int nTargetNum = vecTarget.size();
	fwrite(&nTargetNum, sizeof(int), 1, fp);
	fwrite(&vecTarget[0], sizeof(stPointCoodinate), nTargetNum, fp);

	fclose(fp);

	return 0;
}

/*
从文件中读入点数据
*/
int ReadPointsFromFile(const std::string& binFile, std::vector<stPointCoodinate>& vecTarget)
{
	FILE* fp = fopen(binFile.c_str(), "rb");
	if (NULL == fp)
	{
		printf("point file open failed!\n");
		return -1;
	}
	int nTargetNum = 0;
	fread(&nTargetNum, sizeof(int), 1, fp);
	vecTarget.resize(nTargetNum);
	fread(&vecTarget[0], sizeof(stPointCoodinate), nTargetNum, fp);

	fclose(fp);

	return 0;
}

/*
测试点文件的读写
*/
void TestPointFileRW()
{
	std::vector<stPointCoodinate> vecTarget;
	for (int i = 0; i < 5; i++)
	{
		stPointCoodinate pt;
		pt.m_CoodinateX = 100.0 + i * 10.0;
		pt.m_CoodinateY = 100.0 + i * 10.0;
		vecTarget.push_back(pt);
	}

#if defined(_WIN32) || defined(_WIN64)

	std::string binFile = "D:\\TestData\\test_point.pt";

#else

	std::string binFile = "/home/lx/TestData/test_point.pt";

#endif

	int ret = WritePointsToFile(vecTarget, binFile);

	vecTarget.clear();

	ret = ReadPointsFromFile(binFile, vecTarget);

	if (!vecTarget.empty())
	{
		int num = vecTarget.size();
		for (int i = 0; i < num; i++)
		{
			printf("%f,%f \n", vecTarget[i].m_CoodinateX, vecTarget[i].m_CoodinateY);
		}
	}
}

int main(int argc, char* argv[])
{
	TestPointFileRW();

	getchar();
    return 0;
}

windows效果图如下：

linux效果图如下：