expected ‘struct matrix_t *’ but argument is of type ‘struct matrix_t *’ ?_? no difference

Question

main.c:78:25: erreur: assignment from incompatible pointer type [-Werror]
main.c:81:9: erreur: passing argument 2 of ‘matrix_multiply’ from incompatible pointer type         


        

Answer 1

Your type definition should read

typedef struct matrix_t {
   int **M;
   int nLi;
   int nCo;
   struct matrix_t *next;
} matrix_t;

Otherwise, the type matrix_t refers to a complete but unnamed structure type, whereas struct matrix_t refers to a different, named but incomplete structure type which you never define.

Answer 2

Aha, you don't have a struct matrix_t yet the next field is declared using a struct tag. This then causes problems whenever the next field is used.

matrix_t could be both a struct tag and a type name, as they are in different namespaces, but as it is, your definition starts with...

struct {

not...

struct matrix_t {

In other words, you have an unnamed struct which has a typedef called matrix_t but you never actually define a struct matrix_t.

Answer 3

Change your struct definition to this:

typedef struct matrix_t {
   int **M;
   int nLi;
   int nCo;
   struct matrix_t *next;
} matrix_t;

Notice the difference?

struct matrix_t is not the same as typedef ... matrix_t; they exist in different namespaces; so in your version of the code, the compiler assumes that struct matrix_t *next refers to a different, incomplete type.