Undefined symbols for architecture i386:

I've recently moved over to a mac, and am struggling using the command line compilers. I'm using g++ to compile, and this builds a single source file开发者_运维百科 fine. if I try to add a custom header file, when I try to compile using g++ I get undefined symbols for architecture i386. The programs compile fine in xCode however. Am I missing something obvious?

tried using g++ -m32 main.cpp... didn't know what else to try.

Okay, The old code compiled... Have narrowed it down to my constructors.

class Matrix{
public:
    int a;
    int deter;

    Matrix();
    int det();
};

#include "matrix.h"


Matrix::Matrix(){
    a = 0;
    deter = 0;
}

int Matrix::det(){
    return 0;

}

my error is Undefined symbols for architecture x86_64: "Matrix::Matrix()", referenced from: _main in ccBWK2wB.o ld: symbol(s) not found for architecture x86_64 collect2: ld returned 1 exit status

my main code has

#include "matrix.h"
int main(){
    Matrix m;

    return 0;
} 

along with the usual

It looks like you’ve got three files:

• matrix.h, a header file that declares the Matrix class;
• matrix.cpp, a source file that implements Matrix methods;
• main.cpp, a source file that defines main() and uses the Matrix class.

In order to produce an executable with all symbols, you need to compile both .cpp files and link them together.

An easy way to do this is to specify them both in your g++ or clang++ invocation. For instance:

clang++ matrix.cpp main.cpp -o programName

or, if you prefer to use g++ — which Apple haven’t updated in a while, and it looks like they won’t in the foreseeable future:

g++ matrix.cpp main.cpp -o programName

is not the case here, but it may happen to be the you forget to put the class name with ::

for example:

a good format:

foo.h

class Foo{
public:
    Foo();
    void say();
private:
    int x;
};

foo.cpp

Foo::Foo(){
    this->x = 1;
}

void Foo::say(){
    printf("I said!\n");
}

a bad format

foo.h

class Foo{
public:
    Foo();
    void say();
private:
    int x;
}

foo.cpp

Foo::Foo(){
    this->x = 1;
}

//I always mistake here because I forget to put the class name with :: and the xcode don't show this error.
void say(){
    printf("I said!\n");
}

Did you actually define the Box constructor somewhere? (like Line.cpp)