下载图片 有时网络卡, 图片只有半张, 用这个IsCompletedImage可以检查下载的图片是否完整, 可以检查jpg, bmp, gif, png.主要根据图片开头和结尾的特定字节来判断的.
static void Main(string[] args){string strFileName = @"c:\test.jpg";if (IsCompletedImage(strFileName)){Console.WriteLine("完整图片");}elseConsole.WriteLine("残缺图片");Console.ReadKey();}private static bool IsCompletedImage(string strFileName)
{try{FileStream fs = new FileStream(strFileName, FileMode.Open);BinaryReader reader = new BinaryReader(fs);try{byte[] szBuffer = reader.ReadBytes((int)fs.Length);//jpg png图是根据最前面和最后面特殊字节确定. bmp根据文件长度确定//png检查if (szBuffer[0] == 137 && szBuffer[1] == 80 && szBuffer[2] == 78 && szBuffer[3] == 71 && szBuffer[4] == 13&& szBuffer[5] == 10 && szBuffer[6] == 26 && szBuffer[7] == 10){//&& szBuffer[szBuffer.Length - 8] == 73 && szBuffer[szBuffer.Length - 7] == 69 && szBuffer[szBuffer.Length - 6] == 78if (szBuffer[szBuffer.Length - 5] == 68 && szBuffer[szBuffer.Length - 4] == 174 && szBuffer[szBuffer.Length - 3] == 66&& szBuffer[szBuffer.Length - 2] == 96 && szBuffer[szBuffer.Length - 1] == 130)return true;//有些情况最后多了些没用的字节for (int i = szBuffer.Length - 1; i > szBuffer.Length / 2; --i){if (szBuffer[i - 5] == 68 && szBuffer[i - 4] == 174 && szBuffer[i - 3] == 66&& szBuffer[i - 2] == 96 && szBuffer[i - 1] == 130)return true;}}else if (szBuffer[0] == 66 && szBuffer[1] == 77)//bmp{//bmp长度//整数转成字符串拼接string str = Convert.ToString(szBuffer[5], 16) + Convert.ToString(szBuffer[4], 16)+ Convert.ToString(szBuffer[3], 16) + Convert.ToString(szBuffer[2], 16);int iLength = Convert.ToInt32("0x" + str, 16); //16进制数转成整数if (iLength <= szBuffer.Length) //有些图比实际要长return true;}else if (szBuffer[0] == 71 && szBuffer[1] == 73 && szBuffer[2] == 70 && szBuffer[3] == 56)//gif{//标准gif 检查00 3Bif (szBuffer[szBuffer.Length - 2] == 0 && szBuffer[szBuffer.Length - 1] == 59)return true;//检查含00 3Bfor (int i = szBuffer.Length - 1; i > szBuffer.Length / 2; --i){if (szBuffer[i] != 0){if (szBuffer[i] == 59 && szBuffer[i - 1] == 0)return true;}}}else if (szBuffer[0] == 255 && szBuffer[1] == 216) //jpg{//标准jpeg最后出现ff d9if (szBuffer[szBuffer.Length - 2] == 255 && szBuffer[szBuffer.Length - 1] == 217)return true;else{//有好多jpg最后被人为补了些字符也能打得开, 算作完整jpg, ffd9出现在近末端//jpeg开始几个是特殊字节, 所以最后大于10就行了 从最后字符遍历//有些文件会出现两个ffd9 后半部分ffd9才行for (int i = szBuffer.Length - 2; i > szBuffer.Length / 2; --i){//检查有没有ffd9连在一起的if (szBuffer[i] == 255 && szBuffer[i + 1] == 217)return true;}}}}catch{}finally{if (fs != null)fs.Close();if (reader != null)reader.Close();}}catch{return false;}return false;
}