Interesting callback function

typedef void( *fp_t )(char *);

fp_t( *fp) [2];

It is easy to understand to expand it shown as the following.

void(*(*fp)[4])(char*);

Here is an example to show  where this callback function can be used.

#include <stdio.h>

typedef void( *fp_t )(char *);

void  spi_read(char *data)
{
printf ("spi_read\n");
}
void  spi_write(char *data)
{
printf ("spi_write\n");
}
void  nand_read(char *data)
{
printf ("nand_read\n");
}
void  nand_write(char *data)
{
printf ("nand_write\n");
}
void (*spi_fp[2]) (char *);
void (*nand_fp[2]) (char *);
int main()
{
    int i;
 
    fp_t( *fp) [2];
    spi_fp[0] = spi_read;    
    spi_fp[1] = spi_write;    
    nand_fp[0] = nand_read;    
    nand_fp[1] = nand_write;    
    
    fp = &spi_fp;
    for (i=0;i<2;i++)
    {
        (*fp)[i] (0);
    }
    return 0;
}