Is declaring a pointer and assigning the result of a realloc to it as an if argument valid in C?

Question

I am trying to implement the Dijkstra algorithm, and I first need to design a graph structure with variable number of nodes; in order to do so, I'll need to dynamically change the size of an array of structures, and I wanted to know if writing this :

if( !(struct s *a = (struct s *)realloc(some_pointer_to_s_struct, new_size*sizeof(struct s))) ) {
    return -1; //because that means my pointer is NULL
}
//do something

is correct in C, because according to this post : answer to a post on the subject it is.

However when I tried to change my code to match that pattern, I get plenty of error: expected ‘)’ before xxx and other errors of the sort... I thought that maybe I forgot to match a bracket or a parenthesis at first, but I spent a good 30 minutes reviewing my code, and that doesn't seem to be the issue.

The post you link is **C++**. C is a **different language**. They are similar enough, but you can't deduce something is valid in C just because it's valid in C++ (or vice versa). Beyond that, your attempt is not valid C++ either. — StoryTeller - Unslander Monica, Nov 17 '19 at 11:22
Each line of code - just do one thing at a time. Makes things easier to read and understand. — Ed Heal, Nov 17 '19 at 11:35
In C [you shouldn't cast the result of malloc](https://stackoverflow.com/q/605845/995714), unlike C++ — phuclv, Nov 17 '19 at 13:07

score 2 · Accepted Answer · answered Nov 17 '19 at 11:26

2

That question is about C++ and not about C. In C it isn't possible.

BTW your code isn't valid C++ either as it tries to use a negation on the declaration.

answered Nov 17 '19 at 11:26

AProgrammer

51,233
8
91
143

Yes but the answer, was for C and C++, but you were right it was the negation of the declaration was causing the issue! – Balocre Nov 17 '19 at 11:32
@Balocre - At no point did the poster of the accepted answer claimed it's valid C. – StoryTeller - Unslander Monica Nov 17 '19 at 11:33

Is declaring a pointer and assigning the result of a realloc to it as an if argument valid in C?

1 Answers1