利用fseek和ftell求文件的长度（字节数）

#include<iostream>
using namespace std;

int main()
{
	int offset;
	int fromWhere; // 2表示文件结尾

	FILE *fp = fopen("myData.txt", "w");
	fprintf(fp, "123456");
	fclose(fp);

	fp = fopen("myData.txt", "r");
	offset = 0;
	fromWhere = 2;
	fseek(fp, offset, fromWhere);
	cout << ftell(fp) << endl;
	fclose(fp);

	cout << "*********************" << endl;

	int a[10];
	memset(a, 0, sizeof(a));

	fp = fopen("yourData", "wb");
	fwrite(a, sizeof(a), 1, fp);
	fclose(fp);

	fp = fopen("yourData", "rb");
	fseek(fp, offset, fromWhere);
	cout << ftell(fp) << endl;
	fclose(fp);

	return 0;
}

      结果为：

6
*********************
40

     在视频中，经常要求视频的帧数，现有foreman_qcif.yuv文件，帧数为300，且看下面程序：（x264中就是这么求的）

#include <stdio.h>

// yuv文件结构体
typedef struct yuvFile
{
	FILE *fp;
	int width;
	int height;
}YUVFILE;

// 获取yuv文件的帧数
int getFrameTotalYuv(YUVFILE file)
{
    int frameTotal;
	int size;

    if( !fseek( file.fp, 0, SEEK_END ) )
    {
        size = ftell( file.fp );
        frameTotal = size/( file.width * file.height * 3 / 2 ); // yuv420
    }

    return frameTotal;
}

int main()
{
	YUVFILE file;

	file.fp = fopen("foreman_qcif.yuv", "rb");
	file.width = 176;
	file.height = 144;

	printf("%d
", getFrameTotalYuv(file));

	return 0;
}

       结果为：300