I am trying to draw a quad with texturing. The texture should not be pure green (see vector<float> pixel_data).

My source is:

void draw_objects(void)
{
	glDisable(GL_LIGHTING);

	float projection_modelview_mat[16];

	init_perspective_camera(45.0f,
		float(win_x) / float(win_y),
		0.01f, 10000.0f,
		0, 0, 10, // Camera position.
		0, 0, 0, // Look at position.
		0, 1, 0, // Up direction vector.
		projection_modelview_mat);

	glActiveTexture(GL_TEXTURE0);
	glGenTextures(1, &card_tex);
	glBindTexture(GL_TEXTURE_2D, card_tex);
	glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST);
	glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_NEAREST);

	vector<float> pixel_data;
	pixel_data.push_back(0);
	pixel_data.push_back(1);
	pixel_data.push_back(0);

	pixel_data.push_back(1);
	pixel_data.push_back(1);
	pixel_data.push_back(0);
	
	pixel_data.push_back(0);
	pixel_data.push_back(1);
	pixel_data.push_back(1);
	
	pixel_data.push_back(1);
	pixel_data.push_back(0);
	pixel_data.push_back(1);

	glTexImage2D(GL_TEXTURE_2D, 0, GL_RGB32F, 2, 2,
		0, GL_RGB,
		GL_FLOAT, &pixel_data[0]);

	perspective_tex.use_program();

	glUniformMatrix4fv(glGetUniformLocation(perspective_tex.get_program(), "mvp_matrix"), 1, GL_FALSE, &projection_modelview_mat[0]);
	glUniform1i(glGetUniformLocation(perspective_tex.get_program(), "tex"), 0);

	glGenBuffers(1, &triangle_buffer);

	vector<GLfloat> vertex_data = {

		// 3D position, 2D texture coordinate

		// card front
		-1, -1,  0.0, 0, 0, // vertex 0
		 1, -1,  0.0,  0, 1.0, // vertex 1
		 1,  1,  0.0,  1.0, 1.0, // vertex 2
		-1, -1,  0.0,  0, 0, // vertex 0
		 1,  1,  0.0,  1.0, 1.0, // vertex 2
		-1,  1,  0.0,  1.0, 0, // vertex 3
	};

	const GLuint components_per_vertex = 5;
	const GLuint components_per_position = 3;
	const GLuint components_per_tex_coord = 2;
	const GLuint num_vertices = vertex_data.size() / components_per_vertex;

	glBindBuffer(GL_ARRAY_BUFFER, triangle_buffer);

	glBufferData(GL_ARRAY_BUFFER, vertex_data.size() * sizeof(GLfloat), &vertex_data[0], GL_STATIC_DRAW);

	glEnableVertexAttribArray(glGetAttribLocation(perspective_tex.get_program(), "position"));
	glVertexAttribPointer(glGetAttribLocation(perspective_tex.get_program(), "position"),
		components_per_position,
		GL_FLOAT,
		GL_FALSE,
		components_per_vertex * sizeof(GLfloat),
		NULL);

	glEnableVertexAttribArray(glGetAttribLocation(perspective_tex.get_program(), "tex_coord"));
	glVertexAttribPointer(glGetAttribLocation(perspective_tex.get_program(), "tex_coord"),
		components_per_tex_coord,
		GL_FLOAT,
		GL_TRUE,
		components_per_vertex * sizeof(GLfloat),
		(const GLvoid*)(components_per_position * sizeof(GLfloat)));

	glDrawArrays(GL_TRIANGLES, 0, num_vertices);
}

My vertex shader is:

#version 430
layout(location = 0) in vec3 position;
layout(location = 1) in vec2 texcoord;
uniform mat4 mvp_matrix;
out vec2 ftexcoord;

void main()
{
    ftexcoord = texcoord;
    gl_Position = mvp_matrix*vec4(position, 1);
}

My fragment shader is:

#version 430

uniform sampler2D tex; // texture uniform

in vec2 ftexcoord;

layout(location = 0) out vec4 FragColor;

void main() 
{
   FragColor = texture(tex, ftexcoord);
}

Thank you so much for the solution. It was indeed the typo.