double star before a variable? * *

[dnnymak]

I am trying to read a .pgm file into an array. The code I was given has the following variable declaration:

int **image;

what does the "**" mean before image?


thanks,
Dnnymak

 

[AtomicChip]

The ** denotes a pointer to a pointer. Check out

http://www.cplusplus.com/doc/tutorial/tut3-3.html

for more info.

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[ArkM]

There is a very simple rule to read (all!) C/C++ declarators.

Let's suppose we see this declarator (**image) in an expression. What can we dereference with * operator in C/C++ language? Only pointers, of course. Well, image is a pointer. We have two * operators (right to left binding). So the result of the 1st (right side op must be dereferenced i.e. it's a pointer too. OK, image var must be pointer to pointer.

Now see on a simple type starting this declaration (char). Result of two dereferencing ops (*(*)) must be char.

Conclusion: we have (we declare) pointer to pointer to char!

Try to apply this rule in other cases (for typedefs too). It works...

 

[xwb]

There is also a minor point of style. Some people write

char** image, wow;

Others write

char **image, wow;

They both mean the same thing but the former implies that wow is a char** when it is actually a char. When your in the depths of debugging, such declarations don't help. With the latter, it is obvious that it is a char. If you are going to use the first format, declare your variables separately

char** image;
char wow;

 

[dnnymak]

Great, thanks for the help!!