C：如何为我的类型化结构分配值？

Question

Following jldupont's answer on defining variables with varying data, I defined the following:

enum buffer_format
{ 
    FIFO_U8T = 0, 
    FIFO_U16T 
};

struct buffer_param
{
    enum buffer_format type;
    union
    {
        struct buffer_fifo_u8_t *fifo_u8;
        struct buffer_fifo_u16_t *fifo_u16;
    } is;
};

I then coded the following assignments:

struct buffer_param fifo_uartTx_param;
fifo_uartTx_param.is.fifo_u8 = &fifo_uartTx;
fifo_uartTx_param.type = FIFO_U8T;

However, I am met with some errors that complain that I can't simply reach into my buffer_param type struct to make these assignments. How would I assign the pointer to the UART fifo and set its type?

error: expected '=', ',', ';', 'asm' or '__attribute__' before '.' token
 fifo_uartTx_param.is.fifo_u8 = &fifo_uartTx;
                  ^
error: expected '=', ',', ';', 'asm' or '__attribute__' before '.' token
 fifo_uartTx_param.type = FIFO_U8T;
                  ^

Answer 1

You're getting an error because you're attempting to do assignments outside of a function. Only definitions with an initializer are allowed.

To initialize this variable, do this:

struct buffer_param fifo_uartTx_param = 
    { .type = FIFO_U8T, .is= { .fifo_u8 = &fifo_uartTx } };