How do I explicitly initialize a structure's member vector? [duplicate]

This question already has answers here: Closed 11 years ago.

Possible Duplicate:

how-to initialize 'const std::vector<T>' like a c array

What's the proper syntax to provide an explicit initializer for a std::vector when it's a member of a structure? Here's the structure:

struct pattern_info
    {
        std::string pattern;
        std::vector<std::string> patterns;
    };

Here's how I would like to initialize it (the ??? is the part I'm not sure about):

pattern_info p = { "", ??? };

I know that {} will provide a reasonable default for all the structure members, but I prefer not to do that.

When I compile with -std=c++0x I can do this (and it seems to work):

开发者_高级运维

pattern_info p = { "", {} };

I'm using gcc version 4.4.5 (Debian 4.4.5-8) and would like to do this without the -std=c++0x option.

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Only C++ 0x's std::vector has such initializers. In current C++, you have to use an existing vector, like this ...

std::vector<T> foo;
...push_back...push...push...

const std::vector<T> target = foo;

... or use workarounds like boost::assign.

A second alternative is to use one of std::vector's alternative constructors. One of them is a template and takes an input-iterator range:

const int foo[] = { 1, 1, 2, 3, 5, 8, 13 };
const std::vector<int> bar (foo, 
                            foo + (sizeof foo / sizeof *foo));

---

This is only possible in C++0x, as already stated. As an alternative, you could use Boost. Take a look at the example given in the introduction:
> http://www.boost.org/doc/libs/1_39_0/libs/assign/doc/#intro

---

If vector is going to be empty (as shown in your c++0x example version) then,

pattern_info p = { "" };

I think, you can even skip to put "" for std::string too. If you want non-empty string then only initialize. To get rid of compiler warning, you may try:

pattern_info p = {};

Edit: If you want to get away with the warnings then provide a default constructor.

struct pattern_info
{
//...
  pattern_info() : pattern(""), patterns(0) {}
};

And declare as it is:

pattern_info p;