I can remember the first time I wrote my Obj Mesh loader. It took hours. Today I needed also an obj mesh loader and this time it took mere minutes (under 15 minutes at least), so I have decided to share it. Keep in mind you should most likely separate it in header and source files.

/**
 * The MIT License
 *
 * Copyright (c) 2010 Wouter Lindenhof (http://limegarden.net)
 *
 * Permission is hereby granted, free of charge, to any person obtaining a copy
 * of this software and associated documentation files (the "Software"), to deal
 * in the Software without restriction, including without limitation the rights
 * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
 * copies of the Software, and to permit persons to whom the Software is
 * furnished to do so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice shall be included in
 * all copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
 * THE SOFTWARE.
 */
#include <string>
#include <vector>
#include <sstream>
#include <fstream>

#define TOKEN_VERTEX_POS "v"
#define TOKEN_VERTEX_NOR "vn"
#define TOKEN_VERTEX_TEX "vt"
#define TOKEN_FACE "f"

struct Vector2f{
    float x, y;
};
struct Vector3f{
    float x, y, z;
};

struct ObjMeshVertex{
    Vector3f pos;
    Vector2f texcoord;
    Vector3f normal;
};

/* This is a triangle, that we can render */
struct ObjMeshFace{
    ObjMeshVertex vertices[3];
};

/* This contains a list of triangles */
struct ObjMesh{
    std::vector<ObjMeshFace> faces;
};

/* Internal structure */
struct _ObjMeshFaceIndex{
    int pos_index[3];
    int tex_index[3];
    int nor_index[3];
};

/* Call this function to load a model, only loads trianglized meshes */
ObjMesh LoadObjMesh(std::string filename){
    ObjMesh myMesh;

    std::vector<Vector3f>           positions;
    std::vector<Vector2f>           texcoords;
    std::vector<Vector3f>           normals;
    std::vector<_ObjMeshFaceIndex>  faces;
    /**
     * Load file, parse it
     * Lines beginning with:
     * '#'  are comments can be ignored
     * 'v'  are vertices positions (3 floats that can be positive or negative)
     * 'vt' are vertices texcoords (2 floats that can be positive or negative)
     * 'vn' are vertices normals   (3 floats that can be positive or negative)
     * 'f'  are faces, 3 values that contain 3 values which are separated by / and <space>
     */

    char char_buffer[256];
    std::ifstream filestream;
    filestream.open(filename.c_str());
    while(filestream.eof() == false && filestream.bad() == false){
        memset(char_buffer, 0, 256);
        filestream.getline(char_buffer, 256);
        /* FIXED:
         * Where strlen stood was first 256, however this would cause a problem
         * when you only have a token
         */
        std::stringstream str_stream(std::string(char_buffer, strlen(char_buffer)));
        std::string type_str;
        str_stream >> type_str;
        if(type_str == TOKEN_VERTEX_POS){
            Vector3f pos;
            str_stream >> pos.x >> pos.y >> pos.z;
            positions.push_back(pos);
        }else if(type_str == TOKEN_VERTEX_TEX){
            Vector2f tex;
            str_stream >> tex.x >> tex.y;
            texcoords.push_back(tex);
        }else if(type_str == TOKEN_VERTEX_NOR){
            Vector3f nor;
            str_stream >> nor.x >> nor.y >> nor.z;
            normals.push_back(nor);
        }else if(type_str == TOKEN_FACE){
            _ObjMeshFaceIndex face_index;
            char interupt;
            for(int i = 0; i < 3; ++i){
                str_stream >>  face_index.pos_index[i] >> interupt
                           >> face_index.tex_index[i]  >> interupt
                           >> face_index.nor_index[i];
            }
            faces.push_back(face_index);
        }
    }
    filestream.close();

    for(size_t i = 0; i < faces.size(); ++i){
        ObjMeshFace face;
        for(size_t j = 0; j < 3; ++j){
            face.vertices[j].pos        = positions[faces[i].pos_index[j] - 1];
            face.vertices[j].texcoord   = texcoords[faces[i].tex_index[j] - 1];
            face.vertices[j].normal     = normals[faces[i].nor_index[j] - 1];
        }
        myMesh.faces.push_back(face);
    }

    return myMesh;
}