Returning structs inside a class - class

Question

I am converting my application to an OOP type but I am having problem with helper functions. What I did was place helper functions inside the class as private. How should I declare a function "addSection" to return a struct
This is for my .cpp file
section_t XIniFile::*addSection(ini_file_t *n, char *d)
{
section_t *s = (section_t *)malloc(sizeof(section_t *);
//add sections
return s;
}
This is for my .h file
class XIniFile
{
public:
int open(const char *);
int readString(const char *, const char *, char *);
int readInt(const char *, const char *, int *);
int writeString(const char *, const char *, char *);
int writeInt(const char *, const char *, int *);
int close();
private:
typedef struct key_tag {
char *name;
char *value;
key_tag *next;
} key_tag_t;
typedef struct sections_tag {
char *name;
sections_tag *next;
key_tag_t *keys;
} section_t;
typedef struct {
char *name;
section_t *sections;
int modified;
} ini_file_t;
section_t *add_section(ini_file_t *, char *);
key_tag_t *add_key(section_t *, char *, char *);
};
There are a lot of errors but I would like to start first from the first error which is error: ‘section_t’ does not name a type

Answer 1

turn add_section into:
XIniFile::section_t * XIniFile::add_section(ini_file_t *n, char *d)
since section_t is a member of XIniFile

Answer 2

Your struct section_t and other structs need to be declared above the functions that use them, like add_section. C++ type declarations are forward visible, meaning their visibility extend from the point they are first declared onward, but not behind. Order matters, it is an inherited trait of the C language, based on "textual" treatment of include files as opposed to true modules or multi file type metadata, where the compiler traditionally notes each type as it is declared syntactically, stores it in a symbol table, where it is immediately available.
This differs from Java or C# compilers which parse the whole source file first, then resolve types and symbols later, removing order from the equation.
Another error, your * is in the wrong place, move it to directly after section_t:
section_t XIniFile::*addSection(ini_file_t *n, char *d)
Change to:
XIniFile::section_t* XIniFile::addSection(ini_file_t *n, char *d)
Also, in C++ you don't have to use typedef for structs as in C. You can simply say:
struct key_tag_t {
char *name;
char *value;
key_tag_t *next;
};
struct section_t {
char *name;
sections_tag *next;
key_tag_t *keys;
};
section_t *add_section(ini_file_t *, char *);
key_tag_t *add_key(section_t *, char *, char *);
structs and classes are implicitly "typedefed" in C++, though there is a minor difference, it isn't relevant.