Issue while using typedef in c program

Question

I have a function as given below:

void deleteNode ( node **my_head, int t_data )
{
 typedef (*my_head) head;    
}

I want to have an alias for the value of the double pointer (*my_head). While compiling I get the following error:

<error: expected '=', ',', ';', 'asm' or '__attribute__' before 'head'>

I do have a workaround but I still need to make this work. Can anyone please help me out with this!!

error: expected '=', ',', ';', 'asm' or 'attribute' before 'head' — Anshul Tripathi
– Anshul Tripathi, Commented Dec 26, 2014 at 6:14
Without using a new variable I want to make an alias for (*my_head). — Anshul Tripathi
– Anshul Tripathi, Commented Dec 26, 2014 at 6:25

P0W · Accepted Answer · 2014-12-26 06:13:45Z

3

You need to alias the type, not the variable name.

typedef node** head;

answered Dec 26, 2014 at 6:13

P0W

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4 Comments

Anshul Tripathi Over a year ago

This does not solve the purpose for this case as I want to use head as (*my_head) and not as a type alias.

P0W Over a year ago

@AnshulTripathi Same problem as others, I too didn't get your question

Anshul Tripathi Over a year ago

Thanks for your reply. I want to use (*my_head) thorugh out my function many times. Therefore, to reduce the effort of typing (*my_head) everytime I want an alias which replaces (*my_head) everytime when I use it in the function.

Anshul Tripathi Over a year ago

I tried this approach but it doesn't work. The pointer (*my_head) remained unchanged when this function returns i.e. using local variable does not change the pointer (*my_head) when the function returns.

µtex · Accepted Answer · 2014-12-26 06:18:06Z

2

syntax for typedef is

typedef <old type name> <new alias>;

so here you should use

typedef node** head

answered Dec 26, 2014 at 6:18

µtex

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3 Comments

Anshul Tripathi Over a year ago

Is there any way out if I want to use head as (*my_head) and not as a type alias?

µtex Over a year ago

what exactly you want to do ?

Anshul Tripathi Over a year ago

Thanks for your reply. I want to use (*my_head) thorugh out my function many times. Therefore, to reduce the effort of typing (*my_head) everytime I want an alias which replaces (*my_head) everytime when I use it in the function.

Sourav Ghosh · Accepted Answer · 2014-12-26 06:28:07Z

0

Kindly notice the nomenclature typedef. It is used in type definition. To be precise, typedef is used to define a new type, not a variable name alias, as you expect.

As per the c99 standard, chapter 6.7.2 type specifiers are

void
char
short
int
long
float
double
signed
unsigned
_Bool
_Complex
_Imaginary
struct-or-union-specifier
enum-specifier
typedef-name

So, you can use typdef for these types. What you're trying is to use typedef with a variable name. That's not allowed.

As others have specified, you have to use typedef in a format

typedef <old type name> <new alias>;

answered Dec 26, 2014 at 6:28

Sourav Ghosh

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9 Comments

Anshul Tripathi Over a year ago

But I still need way out if I want to use head as (*my_head) and not as a type alias?

Sourav Ghosh Over a year ago

@AnshulTripathi I'm not sure if i have understood your requirement. Can you give a brief example?

Anshul Tripathi Over a year ago

I want to use (*my_head) thorugh out my function many times. Therefore, to reduce the effort of typing (*my_head) everytime I want an alias which replaces (*my_head) everytime when I use it in the function.

Sourav Ghosh Over a year ago

@AnshulTripathi well, if it's only about reducing the type effort, and without a new variable, you can try using #define, with a bit of caution with (), {} and ;.

Anshul Tripathi Over a year ago

We can't write macro in local scope of a function. I have to again get a overhead of defining this alias macro at the beginning of the file. Is there no way out of making an alias in the function block itself?

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