Question

I have two structures as shown below

struct server{
    // some members
};

struct msg{
    struct server* servers;
};

Then I do this.

struct msg msg1;
struct server s1,s2;

msg1.servers = (struct server *)malloc(2*sizeof(struct server));
msg1.servers[0] = &s1; // compilation error 
msg1.servers[1] = &s2;  // compilation error

This code does not compile and giving the following error : incompatible types when assigning to type ‘struct server’ from type ‘struct server *’.

What am I doing wrong?

Answer 1

The problem here is that the expression msg1.servers[0] producets a struct server but you’re providing a struct server* (a pointer type vs a non-pointer type). There are two ways to fix this

The first is to simply provide the struct server instances by value as the code expects

msg1.servers[0] = s1;
msg1.servers[1] = s2;

This will work if struct server is a type that behaves properly when copied around.

The second is necessary if you want to continue using struct server* in the struct msg. In this case you need a double pointer to store the server pointers. And you need to adjust your malloc statement appropriately

struct msg{
    struct server** servers;
};

msg1.servers = malloc(2*sizeof(struct server*));
msg1.servers[0] = &s1; 
msg1.servers[1] = &s2;