使用visual C ++编译器（Visual Studio 2010）导致变量数组大小出错。如何规避这个问题？

Question

I am experiencing some troubles compiling a c++ file that worked well as a previous build under GCC. The issue is, I am using vectors of variable array size:

unsigned int howmany;
std::vector<int>* array_adresses[howmany]; 

I am currently using the Visual-Studio 2010 C++ compiler to built Matlab 64-bit Mex-Files. Since VC++ won't allow me to use arrays whose size is unknown at compile time, I am receiving the following error messages:

error 2057: constant expression expected error 2466: error 2133: unknown size

Is there any way to build the 64 bit mex file using a GCC-compiler option or build it with a different 64-bit compiler under Matlab?

Thanks in advance!!

Answer 1

howmany needs to be constant, and needs to be a defined amount, like so:

const unsigned int howmany = 5;
std::vector<int>* array_adresses[howmany];

Or you can define it dynamically like this:

unsigned int howmany = 5;
std::vector<int>* array_adresses = new std::vector<int>[howmany];

Answer 2

C++ standard doesn't allow variable-length arrays. Lets take this code:

int main(int argc, char *argv[])
{
    int a[argc];
    return 0;
}

This compiles fine with g++ foo.cpp , but fails if you require a strict standard compliance.

g++ foo.cpp -std=c++98 -pedantic :

foo.cpp: In function ‘int main(int, char**)’:
foo.cpp:8: warning: ISO C++ forbids variable length array ‘a’

You should use vector<vector<int> *> or vector<int> ** instead as others already suggested.

Answer 3

Simply replace int ptr[howmany]; with vector ptr(howmany);

to obtain also automatic deallocation at the end of the scope