Expected Expression with strcmp

[adiupadhyay03]

struct Person
{
const char *personName;
int personAge;
struct Person* next;
}P;

int comp_person_name(const void *a, const void *b){

int result = strcmp(((P *)a)->personName,((P *)b)->personName);
return result;

}

The above gives me an error in the line with strcmp. It says Expected expression. Can't inderstand why

[weaknessforcats]

You need to typecast to your typename and not your variable name:

int result = strcmp(((Person*)a)->personName, ((Person*)b)->personName);

[adiupadhyay03]

I tried doing that also, but then it complains

part4.c:19:24: error: use of undeclared identifier 'Person'
int result = strcmp(((Person *)a)->personName,((Person *)b)->per...
^
part4.c:19:32: error: expected expression
int result = strcmp(((Person *)a)->personName,((Person *)b)->per...

and I have changed my struct to ->

struct Person
{
const char *personName;
int personAge;
struct Person* next;
};

[donbock]

A cast like (Person *) assumes there is a type named Person. Only a typedef can create a new type name like that. The OP code does not contain a typedef -- it only has a structure definition.

Replace (Person *) with (struct Person *) ... or add a typedef to define Person as a type that is equivalent to struct Person.