c++ - OpenGL shader linking -

after following set of opengl tutorials great didn't let me understand basics, i'm trying basic opengl coding c++. program supposed read vertex , fragment shader , draw triangle.

i error when linking shaders (i suspect error can tracked down compiling of shader though). know shaders read program, changes them doesn't affect error. running:

glgetprogramiv(shaderprogram, gl_link_status, &success); 

i receive error: "link called without attached shader object". programs builds, , triangle shows, not affected shaders.

update

i no longer above error after fixing mistake. complain after glcompileshader():

"error: 0:3 'location' : syntax error parse error"

so imagine has shader files (will add them below). shader files taken tutorial, assumed work.

shader files:

vertex shader:

#version 330                                                              layout (location = 0) in vec3 position;                                   void main()                                                              {                                                                            gl_position = vec4(0.5*position.x, 0.5*position.y, position.z, 1.0);     } 

fragment shader:

#version 330                                                              out vec4 fragcolor;                                                       void main()                                                              {                                                                            fragcolor = vec4(1.0, 0.0, 0.0, 1.0);                                } 

in main function run:

compileshader(); 

attach shaders:

static void addshader(gluint shaderprogram, glenum shadertype, std::string filepath){  //create shader object gluint shaderobj = glcreateshader(shadertype); //error if no shader if (shaderobj == 0){     fprintf(stderr, "error creating shader type %d\n", shadertype);     exit(0); }  //"specify source code" //readshaderfile returns shader file string std::string shaderfile = readshaderfile(filepath); const char* shaderfilepointer = shaderfile.c_str(); glint shaderfilelength[1];   shaderfilelength[0] = strlen(shaderfilepointer);  glshadersource(shaderobj, 1, &shaderfilepointer, shaderfilelength);  //compile shader glcompileshader(shaderobj);  //check if compile successful glint success; glgetshaderiv(shaderobj, gl_compile_status, &success); if (!success){     glchar infolog[1024];     glgetshaderinfolog(shaderobj, sizeof(infolog), null, infolog);     fprintf(stderr, "error compiling shader type %d: '%s'\n", shadertype, infolog);     exit(1); }  glattachshader(shaderprogram, shaderobj);  } 

and here functions used:

static void compileshaders(){  //create program gluint shaderprogram = glcreateprogram(); //check error if (shaderprogram == 0){     fprintf(stderr, "error creating shader program!\n");     exit(1); }  //attach compiled shaders std::string vertexshaderfilepath    = "shaders/colshading.vert"; std::string fragshaderfilepath      = "shaders/colshading.frag";  addshader(shaderprogram, gl_vertex_shader, vertexshaderfilepath); addshader(shaderprogram, gl_fragment_shader, fragshaderfilepath);  glint success = 0; glchar errorlog[1024] = { 0 };  //link shader program gllinkprogram(shaderprogram); //check link error glgetprogramiv(shaderprogram, gl_link_status, &success);  if (success == 0) {     glgetprograminfolog(shaderprogram, sizeof(errorlog), null, errorlog);     fprintf(stderr, "error linking shader program: '%s'\n", errorlog); }  //use linked shader program gluseprogram(shaderprogram); } 

i doubt more of code needed find problem here, let me know. lot in advance!

solution

the first answer below did trick. removed:

layout (location = 0)  

from vertex shader , added:

glbindattriblocation(shaderprogram, 0, "position"); 

before linking.

it seems either hardware or driver doesn't support explicit shader location syntax, require opengl/glsl > 3.3.

to solve this, if samgak's answer doesn't help, still have 2 options:

1. explicitly set locations before linking shader:

this done glbindattriblocation function, , means same have in shader. example:

addshader(shaderprogram, gl_vertex_shader, vertexshaderfilepath); addshader(shaderprogram, gl_fragment_shader, fragshaderfilepath); //...  //define location of attributes glbindattribute(shaderprogram, 0, "position") //bind "in position" location 0  //link shader program gllinkprogram(shaderprogram); 

2. after linking, , while building vaos (or drawing geometry), query location of attributes, , set buffers accordingly:

you glgetattriblocation function.

gluint positionloc = glgetattriblocation(shaderprogram, "position");// ask location of attribute "position  //create buffers , transfer data... glbindbuffer(gl.array_buffer, ...);   glbufferdata(...);  //turns on vertex attribute "position"  glenablevertexattribarray(positionloc);  //set pointer between buffer , attribute  glvertexattribpointer(positionloc,...); 

for performance reasons, first option recommended, doesn't force flush.