Are you doing this on Mac?

Yes, I was doing this on Mac.

Which tutorial did you follow?

The video from this link: https://www.youtube.com/watch?v=bjGJHq3hgi4

Did you follow the other videos in the series.

I restart the program and all things are good at the end of Tutorial 2 – Shader Files. But when I follow the programming in Tutorial 3, the exact errors happen:

Undefined symbols for architecture x86_64:

  "_SOIL_free_image_data", referenced from:

      _main in main.o

  "_SOIL_load_image", referenced from:

      _main in main.o

ld: symbol(s) not found for architecture x86_64

clang: error: linker command failed with exit code 1 (use -v to see invocation).

I think it came from this part of main.cpp, which is:

    unsigned char *image = SOIL_load_image( "resources/images/image1.jpg", &width, &height, 0, SOIL_LOAD_RGBA );

    glTexImage2D( GL_TEXTURE_2D, 0, GL_RGBA, width, height, 0, GL_RGBA, GL_UNSIGNED_BYTE, image );

    glGenerateMipmap( GL_TEXTURE_2D );

    SOIL_free_image_data( image );

    glBindTexture( GL_TEXTURE_2D, 0 );

But I still get no clue to fix it.

I got the answer from this link: http://www.sonarlearning.co.uk/questions.php?question-topic=717, it works now. Thanks.

Fantastic.