C language function parameters and pointers

1 C language function return pointer method
2 When the parameter of C language function is a pointer, note that the pointer cannot point to NULL;
reference:
C language pointer initialization and NULL as an actual parameter when passing into the function
3 c language: how to write a function, Change the value of the passed pointer parameter
4 C language pointer or reference method can change the value of the variable
Reference:
C language function parameter transfer and pointer and reference summary