glGetUniformLocation，glUniform4f

const char* vs  =   "void main()\
                            {\
                                gl_Position = ftransform();\
                            }";
const char* ps  =   "uniform vec4 _color;\
                            void main()\
                            {\
                                gl_FragColor = _color;\
                            }";
GLint program = createProgram(vs, ps);
// According to the variable name _color Get the corresponding in the shader program uniform The position of the variable ,
// The application operates this _colorId, You can change the uniform Variable 
uniform colorId  =   glGetUniformLocation(program,"_color");

// change uniform 
glUseProgram(program);
    glUniform4f(colorId,0,1,0,1);// To call before drawing 
    //.... Code ellipsis 
    glDrawArrays(GL_TRIANGLE_STRIP,0,4);
glUseProgram(0);