C++ GLSL Linking error - c++

Question

I'm developing a 3d Engine and I got some trouble with the GLSL shader in C++.
Vertex shader:
layout(location = 0) in vec3 vertexUP;
layout(location = 1) in vec3 vertexUV;
out vec3 UP;
out vec3 UV;
void main(){
UP = vertexUP;//Without this line, everything works fine
UV = vertexUV;
gl_Position = ftransform();
}
Fragment shader:
in vec3 UP;
in vec3 UV;
out vec3 color;
uniform sampler2D rs0;
uniform sampler2D rs1;
uniform sampler2D rs2;
void main(){
if(UV[2]==0){//Selects between different textures
color = texture( rs0, vec2(UV[0], UV[1]) ).rgb;
}else if(UV[2]==1){
color = texture( rs1, vec2(UV[0], UV[1]) ).rgb;
}else{
color = texture( rs2, vec2(UV[0], UV[1]) ).rgb;
}
if(UP[0]<2){//Test thing
color[0] = 1.0;
}
}
I want to parse the position array (Location 0) to the fragement shader so I can use it for lighting. It Compiles but linking the vertex shader gives a error:
Vertex shader(s) failed to link, Fragment shader(s) linked.
What am I doing wrong?
EDIT:
The code to load the shaders:
GLuint LoadShaders(const char * vertex_file_path,const char * fragment_file_path){
// Create the shaders
GLuint VertexShaderID = glCreateShader(GL_VERTEX_SHADER);
GLuint FragmentShaderID = glCreateShader(GL_FRAGMENT_SHADER);
// Read the Vertex Shader code from the file
std::string VertexShaderCode;
std::ifstream VertexShaderStream(vertex_file_path, std::ios::in);
if(VertexShaderStream.is_open())
{
std::string Line = "";
while(getline(VertexShaderStream, Line))
VertexShaderCode += "\n" + Line;
VertexShaderStream.close();
}
// Read the Fragment Shader code from the file
std::string FragmentShaderCode;
std::ifstream FragmentShaderStream(fragment_file_path, std::ios::in);
if(FragmentShaderStream.is_open()){
std::string Line = "";
while(getline(FragmentShaderStream, Line))
FragmentShaderCode += "\n" + Line;
FragmentShaderStream.close();
}
GLint Result = GL_FALSE;
int InfoLogLength;
// Compile Vertex Shader
printf("Compiling shader : %s\n", vertex_file_path);
char const * VertexSourcePointer = VertexShaderCode.c_str();
glShaderSource(VertexShaderID, 1, &VertexSourcePointer , NULL);
glCompileShader(VertexShaderID);
// Check Vertex Shader
glGetShaderiv(VertexShaderID, GL_COMPILE_STATUS, &Result);
glGetShaderiv(VertexShaderID, GL_INFO_LOG_LENGTH, &InfoLogLength);
std::vector<char> VertexShaderErrorMessage(InfoLogLength);
glGetShaderInfoLog(VertexShaderID, InfoLogLength, NULL, &VertexShaderErrorMessage[0]);
fprintf(stdout, "%s\n", &VertexShaderErrorMessage[0]);
// Compile Fragment Shader
printf("Compiling shader : %s\n", fragment_file_path);
char const * FragmentSourcePointer = FragmentShaderCode.c_str();
glShaderSource(FragmentShaderID, 1, &FragmentSourcePointer , NULL);
glCompileShader(FragmentShaderID);
// Check Fragment Shader
glGetShaderiv(FragmentShaderID, GL_COMPILE_STATUS, &Result);
glGetShaderiv(FragmentShaderID, GL_INFO_LOG_LENGTH, &InfoLogLength);
std::vector<char> FragmentShaderErrorMessage(InfoLogLength);
glGetShaderInfoLog(FragmentShaderID, InfoLogLength, NULL, &FragmentShaderErrorMessage[0]);
fprintf(stdout, "%s\n", &FragmentShaderErrorMessage[0]);
// Link the program
fprintf(stdout, "Linking program\n");
GLuint ProgramID = glCreateProgram();
glAttachShader(ProgramID, VertexShaderID);
glAttachShader(ProgramID, FragmentShaderID);
glLinkProgram(ProgramID);
// Check the program
glGetProgramiv(ProgramID, GL_LINK_STATUS, &Result);
glGetProgramiv(ProgramID, GL_INFO_LOG_LENGTH, &InfoLogLength);
std::vector<char> ProgramErrorMessage(InfoLogLength);
glGetProgramInfoLog(ProgramID, InfoLogLength, NULL, &ProgramErrorMessage[0]);
fprintf(stdout, "%s\n", &ProgramErrorMessage[0]);
glDeleteShader(VertexShaderID);
glDeleteShader(FragmentShaderID);
return ProgramID;
}

Answer 1

You can't do that:
layout(location = 0) in vec3 vertexUP;
layout(location = 1) in vec3 vertexUV;
...
gl_Position = ftransform();
ftransform() uses the builtin gl_Vertex, and the GL spec requires that to alias attribute index 0, so the GL cannot assign the attribute indices without collision.
You really shouldn't mix the old, deprecated builtins with generic attributes. And if you do, you should led the GL assign the attribute locations.