c - 打开宏定义 : tdfx_span. c: 需要左值作为赋值的左操作数

Question

我尝试在 Ubuntu maverick 下编译 X11R6-7.0，遇到了一些我无法自行解决的奇怪编译错误。

我需要 X11R6-7.0，因为 ati 催化剂驱动程序不支持较新的 xorg，而 oss 驱动程序不支持我的硬件的 3d 加速。

有人知道这条错误信息是什么意思吗？我知道一些 C 但我有点困惑。这是否意味着 GET_FB_DATA 宏返回了 NULL 或某些方法/属性未设置？

任何进一步了解如何在这一点上“调试”预处理器定义都会很棒。我不认为我可以使用 #error 打印任何有用的东西。

我得到的错误:

tdfx_span.c: In function ‘tdfxDDWriteDepthPixels’:
tdfx_span.c:976: error: lvalue required as left operand of assignment
tdfx_span.c:1008: error: lvalue required as left operand of assignment
tdfx_span.c: In function ‘write_stencil_pixels’:
tdfx_span.c:1242: error: lvalue required as left operand of assignment

代码:

958-   switch (depth_size) {
959-   case 16:
960-      GetBackBufferInfo(fxMesa, &backBufferInfo);
961-      /*
962-       * Note that the _LOCK macro adds a curly brace,
963-       * and the UNLOCK macro removes it.
964-       */
965-      WRITE_FB_SPAN_LOCK(fxMesa, info,
966-             GR_BUFFER_AUXBUFFER, GR_LFBWRITEMODE_ANY);
967-      {
968-     LFBParameters ReadParams;
969-     GetFbParams(fxMesa, &info, &backBufferInfo,
970-             &ReadParams, sizeof(GLushort));
971-     for (i = 0; i < n; i++) {
972-        if (mask[i] && visible_pixel(fxMesa, x[i], y[i])) {
973-           xpos = x[i] + fxMesa->x_offset;
974-           ypos = bottom - y[i];
975-           d16 = depth[i];
976:           PUT_FB_DATA(&ReadParams, GLushort, xpos, ypos, d16);
977-        }
978-     }
979-      }
980-      WRITE_FB_SPAN_UNLOCK(fxMesa, GR_BUFFER_AUXBUFFER);
981-      break;
982-   case 24:

和相关宏:

#define GET_FB_DATA(ReadParamsp, type, x, y)                        \
   (((x) < (ReadParamsp)->firstWrappedX)                            \
        ? (((type *)((ReadParamsp)->lfbPtr))                        \
                 [(y) * ((ReadParamsp)->LFBStrideInElts)            \
                   + (x)])                                          \
        : (((type *)((ReadParamsp)->lfbWrapPtr))                    \
                 [((y)) * ((ReadParamsp)->LFBStrideInElts)          \
                   + ((x) - (ReadParamsp)->firstWrappedX)]))
#define GET_ORDINARY_FB_DATA(ReadParamsp, type, x, y)               \
    (((type *)((ReadParamsp)->lfbPtr))                              \
                 [(y) * ((ReadParamsp)->LFBStrideInElts)            \
                   + (x)])
#define GET_WRAPPED_FB_DATA(ReadParamsp, type, x, y)                \
    (((type *)((ReadParamsp)->lfbWrapPtr))                          \
                 [((y)) * ((ReadParamsp)->LFBStrideInElts)          \
                   + ((x) - (ReadParamsp)->firstWrappedX)])
#define PUT_FB_DATA(ReadParamsp, type, x, y, value)                        \
    (GET_FB_DATA(ReadParamsp, type, x, y) = (type)(value))
#define PUT_ORDINARY_FB_DATA(ReadParamsp, type, x, y, value)              \
    (GET_ORDINARY_FB_DATA(ReadParamsp, type, x, y) = (type)(value))
#define PUT_WRAPPED_FB_DATA(ReadParamsp, type, x, y, value)                \
    (GET_WRAPPED_FB_DATA(ReadParamsp, type, x, y) = (type)(value))

LFBParameters 结构

483-typedef struct
484-{
485-   void *lfbPtr;
486-   void *lfbWrapPtr;
487-   FxU32 LFBStrideInElts;
488-   GLint firstWrappedX;
489-}
490:LFBParameters;

Answer 1

不，当然这不是因为指针为 0。这表明类型错误。正如消息所说，您需要在赋值的左侧有一个左值。 (这听起来很正常，不是吗？)

我猜想其中一个宏会以某种方式返回一个指针值，而您却没有取消引用它。