fstream获得文件大小

如果是ifstream使用seekg和tellg：

    ifstream fsRead;
    fsRead.open(srcFilePath.c_str(), ios::in|ios::binary);
    if (!fsRead) {
        sec_error("Uncompress processing: can not open source file! [%s]",src_file_name);
        return -3;
    }
    fsRead.seekg(0, fsRead.end);
    size_t srcSize = fsRead.tellg();
    if (!srcSize) {
        sec_error("Source file: [%s] size is 0! Return directly!",srcFilePath.c_str());
        fsRead.close();
        sec_error("File closed successfully!");
        return 0;
    }
    sec_debug("Source file :[%s] size is : [%d]",srcFilePath.c_str(), srcSize);

    ofstream fsWrite;
    fsWrite.open(destFilePath.c_str(), ios::out|ios::binary);
    if (!fsWrite) {
        fsRead.close();
        sec_error("Compress processing: can not open destination file! [%s]",des_file_name);
        return -3;
    }
    // Some work ...
    fsWrite.seekp(0, fsWrite.end);
    size_t dstFileSize = fsWrite.tellp();