opengl - glBindAttribLocation does not work like expected -

i have pretty basic opengl application vertices of single triangle in vao. vertex attributes "p" position , "c" color. shader basic. doesn't transform positions , interpolates colors of 3 vertices on triangle.

the problem occurs when accessing attributes. if position @ location 0 , color @ 1, shader somehow swaps attributes (interpreting color position , vice versa). if color @ 0 , position @ 1, works expected.

i can't figure out, wrong , appreciate help. here code:

...  glint loc_p = 0, loc_c = 1; // works not // glint loc_p = 1, loc_c = 0; // works  glbindattriblocation(shader1, loc_p, "p"); glbindattriblocation(shader1, loc_c, "c");  glvertexattribpointer(loc_p, 4, gl_float, false, 8*sizeof(glfloat), (glvoid*)0); glvertexattribpointer(loc_c, 4, gl_float, false, 8*sizeof(glfloat), (glvoid*)(4*sizeof(glfloat)));  {     glclear(gl_color_buffer_bit | gl_depth_buffer_bit);      // render shader 1     glbindvertexarray(vao);     gluseprogram(shader1);     glenablevertexattribarray(loc_p);     glenablevertexattribarray(loc_c);     gldrawarrays(gl_triangles, 0, 3); } while(running); 

vertex shader:

#version 430  in vec4 p; in vec4 c;  out vec4 fcol;  void main() {     fcol = c;     gl_position = p; } 

fragment shader:

#version 430  in vec4 fcol;  void main() {     gl_fragcolor = fcol; } 

you have link shader program using gllinkprogram after calling glbindattriblocation. opengl website:

any attribute binding occurs after program object has been linked not take effect until next time program object linked.