GLSL Error: (0) : error C5145: must write to gl_Position - c++

Question

When I go to link my compiled vertex and fragment shaders, I get this error:
(0) : error C5145: must write to gl_Position
Here is the basic section of my code where the error occurs:
GLuint vertexShader = glCreateShader(GL_VERTEX_SHADER);
glShaderSource(GL_VERTEX_SHADER, 1, &vertexShaderCode, nullptr);
glCompileShader(GL_VERTEX_SHADER);
GLint okay;
glGetShaderiv(GL_VERTEX_SHADER, GL_COMPILE_STATUS, &okay);
if (okay == GL_FALSE) {
char infoLog[512];
glGetShaderInfoLog(GL_VERTEX_SHADER, 512, nullptr, infoLog);
error("Failed to compile vertex shader.", infoLog);
}
GLuint fragmentShader = glCreateShader(GL_FRAGMENT_SHADER);
glShaderSource(GL_FRAGMENT_SHADER, 1, &fragmentShaderCode, nullptr);
glCompileShader(GL_FRAGMENT_SHADER);
glGetShaderiv(GL_FRAGMENT_SHADER, GL_COMPILE_STATUS, &okay);
if (okay == GL_FALSE) {
char infoLog[512];
glGetShaderInfoLog(GL_FRAGMENT_SHADER, 512, nullptr, infoLog);
error("Failed to compile fragment shader.", infoLog);
}
GLuint shaderProgram = glCreateProgram();
glAttachShader(shaderProgram, vertexShader);
glAttachShader(shaderProgram, fragmentShader);
glLinkProgram(shaderProgram);
glGetProgramiv(shaderProgram, GL_LINK_STATUS, &okay);
if (okay == GL_FALSE) {
char infoLog[512];
glGetProgramInfoLog(shaderProgram, 512, nullptr, infoLog);
error("Failed to link the shader program.", infoLog);
}
glDeleteShader(vertexShader);
glDeleteShader(fragmentShader);
Here is the vertex shader:
#version 330 core
layout (location = 0) in vec3 vertexData;
layout (location = 1) in vec2 textureCoord;
out vec2 textCoord;
uniform mat4 projectionMat;
uniform mat4 viewMat;
uniform mat4 modelMat;
void main() {
gl_Position = projectionMat * viewMat * modelMat * vec4(vertexData, 1.0f);
vertColor = vertexColor;
textCoord = textureCoord;
}
Here is the fragment shader (in case it matters):
#version 330 core
in vec2 textCoord;
out vec4 color;
uniform sampler2D text;
uniform vec4 textColor;
void main() {
color = texture(text, textCoord) * textColor;
}
I did some investigating and toyed around with it and found that (unlike other people) the source I was sending to OpenGL was not empty and was the full, correct source (I found this by printing vertexShaderCode).
How do I fix it?

Answer 1

GLuint vertexShader = glCreateShader(GL_VERTEX_SHADER);
This creates a shader object for a vertex shader. And this means that vertexShader now contains that shader object. Given that:
glShaderSource(GL_VERTEX_SHADER, 1, &vertexShaderCode, nullptr);
What does this do? It's supposed to put the given code into a shader object. But none of the parameters are a shader object. The first parameter is an OpenGL enumerator, which is not a shader object.
Shader and program objects are not like most OpenGL objects. You don't bind them just to set data into them (except for uniforms and programs, but we don't even need to bind them for that since GL 4.1). If you want to manipulate a shader, you have to actually pass the shader to the function that manipulates it.
glShaderSource(vertexShader, 1, &vertexShaderCode, nullptr);