C++ 判断文件内容是二进制还是ASCII

enum FileTypeEnum
{
    FileTypeUnknown,
    FileTypeBinary,
    FileTypeText
};

FileTypeEnum
DetectFileType(const char *filename,
               unsigned long length,
               double percent_bin)
{
    if (!filename || percent_bin < 0)
    {
        return FileTypeUnknown;
    }

    FILE *fp = fopen(filename, "rb");
    if (!fp)
    {
        return FileTypeUnknown;
    }

    // Allocate buffer and read bytes

    unsigned char *buffer = new unsigned char [length];
    size_t read_length = fread(buffer, 1, length, fp);
    fclose(fp);
    if (read_length == 0)
    {
        return FileTypeUnknown;
    }

    // Loop over contents and count

    size_t text_count = 0;

    const unsigned char *ptr = buffer;
    const unsigned char *buffer_end = buffer + read_length;

    while (ptr != buffer_end)
    {
        if ((*ptr >= 0x20 && *ptr <= 0x7F) ||
                *ptr == '\n' ||
                *ptr == '\r' ||
                *ptr == '\t')
        {
            text_count++;
        }
        ptr++;
    }

    delete [] buffer;

    double current_percent_bin =
            (static_cast<double>(read_length - text_count) /
             static_cast<double>(read_length));

    if (current_percent_bin >= percent_bin)
    {
        return FileTypeBinary;
    }

    return FileTypeText;
}

use：

std::cout<<DetectFileType("./testfile/pri3.gpg",256,0.05)<<std::endl;