sizeof single struct member in C

I am not on my development machine right now, but I think you can do one of the following:

sizeof(((parent_t *)0)->text)

sizeof(((parent_t){0}).text)

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Edit: I like the member_size macro Joey suggested using this technique, I think I would use that.

Although defining the buffer size with a #define is one idiomatic way to do it, another would be to use a macro like this:

#define member_size(type, member) sizeof(((type *)0)->member)

and use it like this:

typedef struct
{
    float calc;
    char text[255];
    int used;
} Parent;

typedef struct
{
    char flag;
    char text[member_size(Parent, text)];
    int used;
} Child;

I'm actually a bit surprised that sizeof(((type *)0)->member) is even allowed as a constant expression. Cool stuff.