error: expected initializer before ‘:’ token

Question

I am trying to compile some C++ code (which can be compiled with Visual Studio 2012 on Windows) with g++-4.4.

I have this snippet of code,

const std::string cnw::restoreSession(const std::vector<string> &inNwsFile) {
   for (std::string &nwFile : inNwsFile){
       // some...
   }
}

that I cannot compile because of this error:

CNWController.cpp:154: error: expected initializer before ‘:’ token

Can you give me some advise on how to solve this problem?

Why are you using a colon instead of a semi-colon in the for loop? — David G, May 02 '13 at 15:46
@0x499602D2: Because that's the syntax for C++11's range-based `for`. — Mike Seymour, May 02 '13 at 15:47

Mike Seymour · Accepted Answer · 2013-05-02T16:00:08.280

13

Your compiler is too old to support range-based for syntax. According to GNU it was first supported in GCC 4.6. GCC also requires you to explicitly request C++11 support, by giving the command-line option -std=c++11, or c++0x on compilers as old as yours.

If you can't upgrade, then you'll need the old-school equivalent:

for (auto it = inNwsFile.begin(); it != inNwsFile.end(); ++it) {
    std::string const &nwFile = *it; // const needed because inNwsFile is const
    //some...
}

I believe auto is available in GCC 4.4 (as long as you enable C++0x support), to save you writing std::vector<string>::const_iterator.

If you really do need a non-const reference to the vector's elements then, whichever style of loop you use, you'll need to remove the const from the function parameter.

edited May 02 '13 at 16:00

answered May 02 '13 at 15:46

Mike Seymour

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2

He might also need the `-std=C++11` flag when compiling. – olevegard May 02 '13 at 15:55
3

@olevegard: Indeed, although it's a lower-case `c` and older compilers call it `c++0x`. – Mike Seymour May 02 '13 at 15:58
Thanks Mike, it worked. Yes, I have to use `c++0x`, flag `c++11` is not supported by my compiler. – Aslan986 May 02 '13 at 16:11

error: expected initializer before ‘:’ token

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