[PPM] Comments support

src/pnm.cpp

@@ -70,8 +70,9 @@ public:
 // PPM image file format reader/writer
 class PPM {
 protected:
-    // PPM colored image magic number
+    // binary PPM format constants
     const std::string m_MAGIC_NUMBER = "P6";
+    const char m_COMMENT_CHAR = '#';
 
     // image width and height
     uint32_t m_width;
@@ -80,6 +81,9 @@ protected:
     // maximum value for all color channels
     uint16_t m_max_color;
 
+    // stored comments
+    std::vector<std::string> m_comments;
+
     // actual pixel data
     std::vector<RGB> m_pixel_data;
 
@@ -117,6 +121,16 @@ public:
         m_pixel_data.at(i) = color;
     }
 
+    // Add comment line to the image
+    void add_comment(std::string comment) {
+        m_comments.push_back(comment);
+    }
+
+    // Return all captured comments of an image
+    std::vector<std::string> get_comments() {
+        return m_comments;
+    }
+
     // Read PPM image from disk
     void read(std::string path) {
         // try to open file
@@ -133,21 +147,49 @@ public:
             throw std::runtime_error("Does not have a magic number");
         }
 
-        // width, height, max color
-        ppm_image_file >> entity;
-        m_width = std::stoi(entity);
-
-        ppm_image_file >> entity;
-        m_height = std::stoi(entity);
-
-        ppm_image_file >> entity;
-        m_max_color = std::stoi(entity);
-
+        // width, height, max color while ignoring comments
+        uint8_t captured = 0;
+        while(captured < 3) {
+            ppm_image_file >> entity;
+            if (entity[0] == m_COMMENT_CHAR) {
+                // this is a comment, skip this line
+                getline(ppm_image_file, entity);
+                m_comments.push_back(entity);
+                continue;
+            }
+            
+            switch(captured) {
+                case 0:
+                    // width
+                    m_width = std::stoi(entity);
+                    break;
+                
+                case 1:
+                    // height
+                    m_height = std::stoi(entity);
+                    break;
+                
+                case 2:
+                    // max color
+                    m_max_color = std::stoi(entity);
+                    break;
+            }
+            captured++;
+        }
         m_pixel_data.resize(m_width * m_height);
 
-        // skip one byte
-        char one[1];
-        ppm_image_file.read(one, 1);
+        while(true) {
+            // skip one final byte...
+            char one[1];
+            ppm_image_file.read(one, 1);
+            if (one[0] == m_COMMENT_CHAR) {
+                // ah, comment again...
+                getline(ppm_image_file, entity);
+                m_comments.push_back(entity);
+            } else {
+                break;
+            }
+        }
 
         // retrieve pixels
         char pixel_color[3];
@@ -185,6 +227,11 @@ public:
         // newline
         ppm_image_file << "\n";
 
+        // comments
+        for (const std::string& comment : m_comments) {
+            ppm_image_file << m_COMMENT_CHAR << comment << "\n";
+        }
+
         // width, height, max color value
         ppm_image_file << m_width << " " << m_height << " " << m_max_color << "\n";
 

tests/test.cpp

@@ -54,11 +54,57 @@ void no_pixel_assign() {
     } catch(const std::exception& e) {}
 }
 
+void write_comment() {
+    try {
+        pnm::PPM image;
+        
+        const uint32_t width = 512;
+        const uint32_t height = 512;
+
+        for (uint32_t y = 0; y < height; y++) {
+            for (uint32_t x = 0; x < width; x++) {                
+                image.put_pixel(x, y, pnm::RGB(x / 2, y / 2, x / 2 + y / 2));
+            }
+        }
+
+        image.add_comment("comment 1");
+        image.add_comment("comment 2");
+        image.add_comment("comment \n\n\n");
+
+        image.save("result_image.ppm");
+
+    } catch(const std::exception& e) {
+        std::string error_message("write_comment:", e.what());
+        throw std::runtime_error(error_message);
+    }
+}
+
+void read_comment() {
+    try {
+        write_comment();
+    
+        pnm::PPM image;
+        image.read("result_image.ppm");
+
+        std::vector<std::string> comments = image.get_comments();
+
+        if (comments.size() == 0) {
+            throw std::runtime_error("No comments found, though there should be");
+        }
+        
+    } catch(const std::exception& e) {
+        std::string error_message("read_comment:", e.what());
+        throw std::runtime_error(error_message);
+    }
+}
+
 int main() {
     try {
         make_test_img();
         green_rectangle_on_top_of_existing_image();
         no_pixel_assign();
+        write_comment();
+        read_comment();
 
     } catch(const std::exception& e) {
         std::cout << "[ERROR] " << e.what() << "\n";