How to initialize a struct using the c style while using the g++ compiler?

问题

Generally, in order to initialize a struct in c, we could only specify part of the fields. Like below:

static struct fuse_operations hello_oper = {
    .getattr    = hello_getattr,
    .readdir    = hello_readdir,
    .open       = hello_open,
    .read       = hello_read,
};

However, in C++, we should initialize the variables in the struct without naming the fields. Now, what if I would like to initialize a struct using the c style while using the g++ compiler, how to accomplish this? PS: the reason I need to do this is that the struct fuse_operations has too many fields in it.

回答1:

Unfortunately, even the C++11 version of the C++ standard lacks the designated initializers feature of C99.

回答2:

You wrote:

   static struct fuse_operations hello_oper = {
       .getattr    = hello_getattr,
       .readdir    = hello_readdir,
       .open       = hello_open,
       .read       = hello_read,
   };

Generally, in order to initialize a struct in c, we could only specify part of the fields [...] However, in C++, we should initialize the variables in the struct without naming the fields. Now, what if I would like to initialize a struct using the c style while using the g++ compiler, how to accomplish this? PS: the reason I need to do this is that the struct fuse_operations has too many fields in it.

My solution was to specialize the struct with a constructor:

struct hello_fuse_operations:fuse_operations
{
    hello_fuse_operations ()
    {
        getattr    = hello_getattr;
        readdir    = hello_readdir;
        open       = hello_open;
        read       = hello_read;
    }
}

Then declare a static instance of the new struct:

static struct hello_fuse_operations hello_oper;

Testing worked OK for me (but this depends on the memory layout of the C-struct and C++-struct to be the same -- not sure that's guaranteed)

* UPDATE *

Though this approach worked fine in practice, I have subsequently converted my code to use a utility class, i.e., a class with a single static 'initialize' method that takes a reference to a fuse_operation struct and initializes it. This avoids any possible uncertainty regarding memory layout, and would be my recommended approach in general.

回答3:

maybe you can write a variable param function which takes as input the function pointers and assigns the rest of the attribs as NULL. Since you only have one struct - fuse_operations, you can implement the function for only one struct. something like init_struct(int no_op, ...) wherein you pass function pointers to implementations. Its too complex and laborious, but I suppose you can write it once and use it always...

来源：https://stackoverflow.com/questions/12122234/how-to-initialize-a-struct-using-the-c-style-while-using-the-g-compiler

标签

c++

struct

fuse