带有QDataStream的TGA读取标头

Question

我正在尝试使用Qt QDataStream读取TGA文件头。我从固定类型的规范中具有以下结构：

#pragma pack(push, 1)
/* TGA header */
struct tga_header_t
{
quint8   id_lenght;            /* size of image id */
quint8   colormap_type;        /* 1 is has a colormap */
quint8   image_type;           /* compression type */
/* Color Map Specification */
quint16  cm_origin;            /* colormap origin */
quint16  cm_length;            /* colormap length */
quint8   cm_size;              /* colormap size */
/* Image Specification */
quint16  x_origin;           /* bottom left x coord origin */
quint16  y_origin;           /* bottom left y coord origin */
quint16  width;              /* picture width (in pixels) */
quint16  height;             /* picture height (in pixels) */
quint8   pixel_depth;        /* bits per pixel: 8, 16, 24 or 32 */
quint8   image_descriptor;   /* 24 bits = 0x00; 32 bits = 0x80 */
};
#pragma pack(pop)

我用QFile打开一个文件，然后用它构造一个QDataStream，如下所示：

QFile file(path);
tga_header_t header;
file.open(QIODevice::ReadOnly);
QDataStream stream(&file);
stream >> header.id_lenght >>
header.colormap_type >>
header.image_type >>
header.cm_origin >>
header.cm_length >>
header.cm_size >>
header.x_origin >>
header.y_origin >>
header.width >>
header.height >>
header.pixel_depth >>
header.image_descriptor;
qDebug() << header.id_lenght << "id_lenght" <<
header.colormap_type << "colormap_type" <<
header.image_type << "image_type" <<
header.cm_origin << "cm_origin" <<
header.cm_length << "cm_length" <<
header.cm_size << "cm_size" <<
header.x_origin << "x_origin" <<
header.y_origin << "y_origin" <<
header.width << "width" <<
header.height << "height" <<
header.pixel_depth << "pixel_depth" <<
header.image_descriptor << "image_descriptor" <<
"SIZE:" << sizeof(header);

问题在于我得到的宽度和高度：

0 id_lenght 0 colormap_type 2 image_type 0 cm_origin 0 cm_length 0 cm_size 0 x_origin 0 y_origin 22021 width 3 height 24 pixel_depth 0 image_descriptor SIZE: 18

我应该得到 1366 和 768。如果我十六进制转储文件，我会得到：

0000000 0000 0002 0000 0000 0000 0000 0556 0300
0000010 0018 0000 0000 0000 0000 0000 0000 0000

这很奇怪，因为它在开头有一个额外的字节，而在0x0002和0x0556之间缺少另一个字节。

更新：
使用 fstream 有效，所以如果我错了，请纠正我，但我认为<<运算符没有按我预期工作(仅读取填充结构变量所需的大小(。

stream.read((char*)&header.id_lenght, sizeof(header.id_lenght));
stream.read((char*)&header.colormap_type, sizeof(header.colormap_type));
stream.read((char*)&header.image_type, sizeof(header.image_type));
stream.read((char*)&header.cm_origin, sizeof(header.cm_origin));
stream.read((char*)&header.cm_length, sizeof(header.cm_length));
stream.read((char*)&header.cm_size, sizeof(header.cm_size));
stream.read((char*)&header.x_origin, sizeof(header.x_origin));
stream.read((char*)&header.y_origin, sizeof(header.y_origin));
stream.read((char*)&header.width, sizeof(header.width));
stream.read((char*)&header.height, sizeof(header.height));
stream.read((char*)&header.pixel_depth, sizeof(header.pixel_depth));
stream.read((char*)&header.image_descriptor, sizeof(header.image_descriptor));

使用 QDataStream：：readRawData 也可以：

stream.readRawData((char*)&header.id_lenght, sizeof(header.id_lenght));
stream.readRawData((char*)&header.colormap_type, sizeof(header.colormap_type));
stream.readRawData((char*)&header.image_type, sizeof(header.image_type));
stream.readRawData((char*)&header.cm_origin, sizeof(header.cm_origin));
stream.readRawData((char*)&header.cm_length, sizeof(header.cm_length));
stream.readRawData((char*)&header.cm_size, sizeof(header.cm_size));
stream.readRawData((char*)&header.x_origin, sizeof(header.x_origin));
stream.readRawData((char*)&header.y_origin, sizeof(header.y_origin));
stream.readRawData((char*)&header.width, sizeof(header.width));
stream.readRawData((char*)&header.height, sizeof(header.height));
stream.readRawData((char*)&header.pixel_depth, sizeof(header.pixel_depth));
stream.readRawData((char*)&header.image_descriptor, sizeof(header.image_descriptor));

Answer 1

数据正常。你的电脑将 16 位字解释为小端序。在文件中，它们存储为大端序。

对于所有 16 位类型，您应该交换低/高字节。您也可以使用 Qt： http://doc.qt.io/qt-4.8/qtendian.html 中的辅助函数