CODEWITHSUNDEEP
cstructtypedef
user1174868
user1174868

Reputation:

Calling a node from another file

I know that in programming it is important to keep things simple and be able to be changed. So to me that means it is important to use different files and functions and to keep them separate to easier isolate faults and improve readability.

I am new to C and I don't understand how to do this. I have my nodeTest.h

 #include <stdio.h>
 #include <stdlib.h>

 struct nodeTest
 {
     int data;
     struct nodeTest* next;

 };

Then I have another file trying to call that struct

 #include <stdio.h>
 #include <stdlib.h>
 #include "nodeTest.h"

 nodeTest* first = (nodeTest*)malloc(sizeof(nodeTest));

I am getting an error saying that nodeTest is undeclared(not in function). What does that mean and why can I not use include to include a struct or typedef?

Upvotes: 0

Views: 81

Answers (4)

LihO
LihO

Reputation: 42083

Within global scope, you can just declare / define functions, structures or global variables. You can not call a function just like that (literally "out of nowhere"). Create a mainand call malloc from within:

int main(void) {
    nodeTest* first = (nodeTest*) malloc(sizeof(nodeTest));
    free(first);
    return 0;
}

struct nodeTest {
    int data;
    struct nodeTest* next;
};

defines struct nodeTest so

nodeTest* first;

is unknown to compiler. To solve this you could either use:

struct nodeTest* first;

or even better: use typedef while defining your struct and everything will be fine:

typedef struct nodeTest {
    int data;
    struct nodeTest* next;
} nodeTest ;

Upvotes: 1

Manu343726
Manu343726

Reputation: 14174

You have to use struct NodeTest instead of NodeTest.

Thats because C differentiates three namespaces:

  • Namespace of structs.
  • Namespace of type aliases (type names).
  • Namespace of enums and unions.

So everywhere you want to use an struct, you have to specify the compiler that name refers to an struct. For example:

int main()
{
    struct NodeTest node;
}

One workaround to that problem is to specify an alias to that struct, to "add" the struct to the types namespace:

typedef NodeTest NodeTestType;

int main()
{
    NodeTestType node; //OK
}

Or using the common idiom, declare directly the struct as an alias:

typedef struct { ... } NodeTest;

Note that what this sentence does is to make an alias named NodeTest to an unnamed struct you have declared in the same instruction.
One problem of this approach is that you cannot use the type inside the struct, because its not declared yet. You could workaround it naming the struct:

 typedef struct nodeTest //<-- Note that the struct is not anonimous
 {
     int data;
     struct nodeTest* next;
 } nodeTest;

Upvotes: 2

Charlie Burns
Charlie Burns

Reputation: 7044

Just put your code inside a function like this:

#include <stdio.h>
#include <stdlib.h>
#include "nodeTest.h"

int main(void) {
    struct nodeTest* first = malloc(sizeof(struct nodeTest));
    return 0;
}

Upvotes: 0

Gangadhar
Gangadhar

Reputation: 10516

you need to define nodetest type

typedef struct nodeTest_t
 {
     int data;
     struct nodeTest_t* next;

 }nodeTest;

or else
in main(), use struct keyword before nodeTest.

Upvotes: 0

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