初始化结构数组时，逗号表达式的左操作数无效

Question

This is the pixel_t struct

typedef struct pixelType {
   unsigned char r;          /* red field                  */
   unsigned char g;          /* green field                */
   unsigned char b;          /* blue field                 */
} pixel_t;

I am trying to initialize a list of pixel_t structs but am getting an error saying Left-hand operand of comma expression has no effect. Here is where I initialize it:

pixel_t pixVals[8] = { (pixel_t)(255,255,255), (pixel_t)(255,0,0), (pixel_t)(0,0,255), (pixel_t)(128,0,255), (pixel_t)(0,0,0), (pixel_t)(0,255,0), (pixel_t)(255,128,0), (pixel_t)(255,255,0) };

Any help?

Answer 1

The proper syntax is:

pixel_t pixVals[8] = { {255, 255, 255}, {255, 0, 0}, 

etc. Alternatively, at block scope you can use struct literals: (pixel_t){255, 255, 255} .

When you use parentheses you have an expression using the comma operator, which means to discard all but the rightmost operand.