基于上文进行编程规范：上文.

#include <stdio.h>
#include <stdlib.h>

/*封装一个接口，把数据写入到文件里*/
/*1.注意函数的重用性
  2.注意对于参数的判断
  3.注意格式规范
 */
int saveDataToFile(unsigned char *dataAddr,long dataSize,
                   const char *fileName)
{	
	int nret=0;
	FILE *fp=NULL;
	if (!dataAddr || !fileName)
	{
		printf("wrong dataAddr or fileName\n");
		return -1;
	}
	if (dataSize <= 0)
	{
		printf("wrong dataSize\n");
		return -2;
	}
	fp=fopen(fileName,"wb+");
	if (!fp)
	{
		printf("open file wrong\n");
		return -3;
	}
	nret = fwrite(dataAddr,1,dataSize,fp);
	if (nret < 0)
	{
		printf("write failed\n");
		return -4;
	}
	fclose(fp);
	return 0;
}

/*Y分量数据的值减半 我们也封装成一个接口*/
int halfDataY(const char *dstFileName,const char *srcFileName,
		      long dataSize,long ydataSize)
{
	int		      nRet = 0;
	int 		   nIdx= 0;
	//如果是unsigned int则命名为dwIdx
	unsigned char *dataAddr = NULL;
	FILE          *fp;
	if (!srcFileName || !dstFileName)
	{
		printf("input fileName wrong\n");
		return -1;
	}
	if (dataSize <= 0)
	{
		printf("input dataSize wrong\n");
		return -2;
	}
	dataAddr = (unsigned char *)malloc(dataSize);
	fp = fopen(srcFileName,"rb+");
	if (!fp)
	{
		printf("open file failed\n");
		return -3;
	}
	nRet = fread(dataAddr,1,dataSize,fp);
	if (nRet < 0)
	{
		printf("read file failed\n");
		return -4;
	}
	for (nIdx = 0;nIdx < ydataSize; nIdx++)
	{
		dataAddr[nIdx] = dataAddr[nIdx]/2;
	}
	nRet = saveDataToFile(dataAddr,dataSize,dstFileName);
	if (nRet)
	{
		printf("saveData failed,nRet=%d\n",nRet);
	}
	free(dataAddr);
	fclose(fp);
	return 0;
}

int main()
{
	int nRet = 0;
	halfDataY("new_256x256_yuv420p.yuv","lena_256x256_yuv420p.yuv",
	256*256*3/2,256*256);
	if (nRet)
	{
		printf("halfDataY failed,nRet=%d\n",nRet);
		return -1;
	}
	return 0;
}