Why Can't I build a C++ file using mex?

I have a C++ file that I want to use with my matlab code. The file compiles using mex successfully when I use

mex -c Miguel_2D_unwrapper.cpp

But fails when I use

mex Miguel_2D_unwrapper.cpp

I get the following error:

Error using mex
Cannot export mexFunction: symbol not defined
collect2.exe: error: ld returned 1 exit status

I am sure the problem is not with the code. I am using MinGW and matlab 2017a

[Azuwien aida Bohari]

hi, me to experience the same error. i can compile imnov.c and mex complete successfully but fails when i want to compile comp.c and i get the same error.

Error using mex

Cannot export mexFunction: symbol not defined

collect2.exe: error: ld returned 1 exit status

can someone help me

[Hamza Mahdi]

Hello Azuwein, I ran into the issue because I did not have a mexFunction() in the code. Try modifying your code to be the same as the one you can compile.

Answer 1

[Jan]

Does the file contain the mexFunction() ? The error message tells clearly, that it doesn't.

[Hamza Mahdi]

Do I have to have a mex function? and if I do, what would be the workaround

[Jan]

mex Miguel_2D_unwrapper.cpp tries to compile the file to a Mex file, which is a DLL called from Matlab. The entry point of this call is the function mexFunction(), which must be included in every Mex file. It is equivalent to the main() function in a stand-alone executable.

To solve your problem, you have to explain what your cpp file contains and what it should do. From where do you want to call it? I cannot decide if you have a Mex function, but you have to know this. Anyway, if you want to complile it by mex, you need a mexFunction.

The documentation of mex and the examples in matlabroot\extern\examples\ clarify the details.

[Hamza Mahdi]

Thank you. I will look into it

[sana3 sal]

Hello there, could you please help me by mentioning where i have to but the mexFunction() ? which file? which diectory?

i have this problem when i ran vl_compilenn command to configure the MatConvNet library :

>> vl_compilenn
Building with 'MinGW64 Compiler (C++)'.
Error using mex
Cannot export mexFunction: symbol not defined
Cannot export mexfilerequiredapiversion: symbol not defined
collect2.exe: error: ld returned 1 exit status

Error in vl_compilenn>mex_compile (line 585)
mex(args{:}) ;

Error in vl_compilenn (line 493)
    mex_compile(opts, srcs{i}, objfile, flags) ;

[Bharath Swaminathan]

Check out:

https://in.mathworks.com/help/matlab/apiref/mexfunction.html

and:

https://in.mathworks.com/help/matlab/matlab_external/structure-of-c-mex-function.html