如何强制使用void *结构成员？

Question

I'm trying to cast a void* from a struct member. The struct looks like this:

typedef struct{
    int n;
    void* string;
}query;

And I want to cast the member string to char* and store another string -- lets say str2 --, like this:

char* str2 = "hello";
(*(char*)q.string) = str2;

But it keeps telling me this warning:

example.c: In function 'main': example.c:23:33: warning: assignment makes integer from pointer without a cast [-Wint-conversion] (* (char* )q.string) = str2;

Why is this isn't working?

Answer 1

You don't need a cast, at all.

That said, in your example, query is a type, not a variable.

Use it like

query q;
q.string = str2;

A working example

Answer 2

The warning is correct. Newer versions of gcc have a more helpful message:

warning: assignment to 'char' from 'char *' makes integer from pointer without a cast [-Wint-conversion]

 13 | (*(char*)q.string) = str2; | ^ 

You dereference a char * which gives you a char . To that char type you assign str2 which is of type char * .

As Sourav Ghosh showed you, you can just do this:

q.string = str2;

If you really want to make the cast explicit:

q.string = (void*)str2;

As you see you were doing the cast on the wrong side.