whats the meaning of typedef

[cool17]

Hi
can somebody tell me what does this line means in the c programming "typedef struct terms* express;"?

thank

[tyreld]

The typedef keyword is used to introduce synonyms for types which are intrinsic types (int, float, etc.) or where declared some other way (structs, classes). The new name becomes equivalent to the type you wanted.

 
struct terms {
  // some fields
};
 
// Declare a pointer of struct terms.
struct terms *termptr;
 

Now we accomplish the same thing using a typedef.

 
struct terms {
  // some fields
};
 
typedef struct terms *express;
 
// The decleration of "termptr" is equivalent to our previous example
express termptr;
 

I generally think it is a poor idea to introduce a new type name for pointer types that don't explicitly indicate in the type name that it is a pointer type. In the last example I think it would be better to have named the new type "p_express", or "express_ptr", or "terms_ptr", or "p_terms."

[cool17]

okok thx

but will it be the same as in this case the '*' is in front of the term and not the express

typedef struct terms* express;


so will it make any different?

[cool17]

The code is as follow, thanks again

#ifndef _EXPRESSION_H
#define _EXPRESSION_H


typedef struct terms* express;

typedef struct expressions* myexp;

struct expressions
{
express* exp;
int numberOfTerms;
};

struct terms
{

double x_value;
double x_power;
double x_times;
int positive;
int isX;
int KnowX;

};



myexp createExpression();

void string2Expression(char*,myexp*);

char* expression2String(myexp);


#endif

[m013690]

no, the whitespace does not matter with regard to the pointer declaration.

terms *express
is the same as
terms* express

[tyreld]

okok thx

but will it be the same as in this case the '*' is in front of the term and not the express

typedef struct terms* express;


so will it make any different?

No, there will be no difference.

typedef struct terms *express;
 

is the same as

typedef struct terms* express;
 

is the same as

typedef struct terms * express;
 

It is mostly a matter of personal preference to a certain extent. However, the first example is how most programmers and documentation will write the declaration.

[cool17]

thank guys...