Revisions to How to read MNIST data in C++?

added 196 characters in body

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edited Sep 22, 2016 at 10:09

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uchar** read_mnist_images(string full_path, int& number_of_images, int& image_size) {
    auto reverseInt = [](int i) {
        unsigned char c1, c2, c3, c4;
        c1 = i & 255, c2 = (i >> 8) & 255, c3 = (i >> 16) & 255, c4 = (i >> 24) & 255;
        return ((int)c1 << 24) + ((int)c2 << 16) + ((int)c3 << 8) + c4;
    };

    typedef unsigned char uchar;

    ifstream file(full_path, ios::binary);

    if(file.is_open()) {
        int magic_number = 0, n_rows = 0, n_cols = 0;

        file.read((char *)&magic_number, sizeof(magic_number));
        magic_number = reverseInt(magic_number);

        if(magic_number != 2051) throw runtime_error("Invalid MNIST image file!");

        file.read((char *)&number_of_images, sizeof(number_of_images)), number_of_images = reverseInt(number_of_images);
        file.read((char *)&n_rows, sizeof(n_rows)), n_rows = reverseInt(n_rows);
        file.read((char *)&n_cols, sizeof(n_cols)), n_cols = reverseInt(n_cols);

        image_size = n_rows * n_cols;

        uchar** _dataset = new uchar*[number_of_images];
        for(int i = 0; i < number_of_images; i++) {
            _dataset[i] = new uchar[image_size];
            file.read((char *)_dataset[i], image_size);
        }
        return _dataset;
    } else {
        throw runtime_error("Cannot open file `" + full_path + "`!");
    }
}

uchar* read_mnist_labels(string full_path, int& number_of_labels) {
    auto reverseInt = [](int i) {
        unsigned char c1, c2, c3, c4;
        c1 = i & 255, c2 = (i >> 8) & 255, c3 = (i >> 16) & 255, c4 = (i >> 24) & 255;
        return ((int)c1 << 24) + ((int)c2 << 16) + ((int)c3 << 8) + c4;
    };

    typedef unsigned char uchar;

    ifstream file(full_path, ios::binary);

    if(file.is_open()) {
        int magic_number = 0;
        file.read((char *)&magic_number, sizeof(magic_number));
        magic_number = reverseInt(magic_number);

        if(magic_number != 2049) throw runtime_error("Invalid MNIST label file!");

        file.read((char *)&number_of_labels, sizeof(number_of_labels)), number_of_labels = reverseInt(number_of_labels);

        uchar* _dataset = new uchar[number_of_labels];
        for(int i = 0; i < number_of_labels; i++) {
            file.read((char*)&_dataset[i], 1);
        }
        return _dataset;
    } else {
        throw runtime_error("Unable to open file `" + full_path + "`!");
    }
}

EDIT: Thanks to @Jürgen Brauer for reminding me to correct my answer, although I have fixed it in my code back in time, but forgot to update the answer.

uchar** read_mnist_images(string full_path, int& number_of_images, int& image_size) {
    auto reverseInt = [](int i) {
        unsigned char c1, c2, c3, c4;
        c1 = i & 255, c2 = (i >> 8) & 255, c3 = (i >> 16) & 255, c4 = (i >> 24) & 255;
        return ((int)c1 << 24) + ((int)c2 << 16) + ((int)c3 << 8) + c4;
    };

    typedef unsigned char uchar;

    ifstream file(full_path);

    if(file.is_open()) {
        int magic_number = 0, n_rows = 0, n_cols = 0;

        file.read((char *)&magic_number, sizeof(magic_number));
        magic_number = reverseInt(magic_number);

        if(magic_number != 2051) throw runtime_error("Invalid MNIST image file!");

        file.read((char *)&number_of_images, sizeof(number_of_images)), number_of_images = reverseInt(number_of_images);
        file.read((char *)&n_rows, sizeof(n_rows)), n_rows = reverseInt(n_rows);
        file.read((char *)&n_cols, sizeof(n_cols)), n_cols = reverseInt(n_cols);

        image_size = n_rows * n_cols;

        uchar** _dataset = new uchar*[number_of_images];
        for(int i = 0; i < number_of_images; i++) {
            _dataset[i] = new uchar[image_size];
            file.read((char *)_dataset[i], image_size);
        }
        return _dataset;
    } else {
        throw runtime_error("Cannot open file `" + full_path + "`!");
    }
}

uchar* read_mnist_labels(string full_path, int& number_of_labels) {
    auto reverseInt = [](int i) {
        unsigned char c1, c2, c3, c4;
        c1 = i & 255, c2 = (i >> 8) & 255, c3 = (i >> 16) & 255, c4 = (i >> 24) & 255;
        return ((int)c1 << 24) + ((int)c2 << 16) + ((int)c3 << 8) + c4;
    };

    typedef unsigned char uchar;

    ifstream file(full_path);

    if(file.is_open()) {
        int magic_number = 0;
        file.read((char *)&magic_number, sizeof(magic_number));
        magic_number = reverseInt(magic_number);

        if(magic_number != 2049) throw runtime_error("Invalid MNIST label file!");

        file.read((char *)&number_of_labels, sizeof(number_of_labels)), number_of_labels = reverseInt(number_of_labels);

        uchar* _dataset = new uchar[number_of_labels];
        for(int i = 0; i < number_of_labels; i++) {
            file.read((char*)&_dataset[i], 1);
        }
        return _dataset;
    } else {
        throw runtime_error("Unable to open file `" + full_path + "`!");
    }
}

uchar** read_mnist_images(string full_path, int& number_of_images, int& image_size) {
    auto reverseInt = [](int i) {
        unsigned char c1, c2, c3, c4;
        c1 = i & 255, c2 = (i >> 8) & 255, c3 = (i >> 16) & 255, c4 = (i >> 24) & 255;
        return ((int)c1 << 24) + ((int)c2 << 16) + ((int)c3 << 8) + c4;
    };

    typedef unsigned char uchar;

    ifstream file(full_path, ios::binary);

    if(file.is_open()) {
        int magic_number = 0, n_rows = 0, n_cols = 0;

        file.read((char *)&magic_number, sizeof(magic_number));
        magic_number = reverseInt(magic_number);

        if(magic_number != 2051) throw runtime_error("Invalid MNIST image file!");

        file.read((char *)&number_of_images, sizeof(number_of_images)), number_of_images = reverseInt(number_of_images);
        file.read((char *)&n_rows, sizeof(n_rows)), n_rows = reverseInt(n_rows);
        file.read((char *)&n_cols, sizeof(n_cols)), n_cols = reverseInt(n_cols);

        image_size = n_rows * n_cols;

        uchar** _dataset = new uchar*[number_of_images];
        for(int i = 0; i < number_of_images; i++) {
            _dataset[i] = new uchar[image_size];
            file.read((char *)_dataset[i], image_size);
        }
        return _dataset;
    } else {
        throw runtime_error("Cannot open file `" + full_path + "`!");
    }
}

uchar* read_mnist_labels(string full_path, int& number_of_labels) {
    auto reverseInt = [](int i) {
        unsigned char c1, c2, c3, c4;
        c1 = i & 255, c2 = (i >> 8) & 255, c3 = (i >> 16) & 255, c4 = (i >> 24) & 255;
        return ((int)c1 << 24) + ((int)c2 << 16) + ((int)c3 << 8) + c4;
    };

    typedef unsigned char uchar;

    ifstream file(full_path, ios::binary);

    if(file.is_open()) {
        int magic_number = 0;
        file.read((char *)&magic_number, sizeof(magic_number));
        magic_number = reverseInt(magic_number);

        if(magic_number != 2049) throw runtime_error("Invalid MNIST label file!");

        file.read((char *)&number_of_labels, sizeof(number_of_labels)), number_of_labels = reverseInt(number_of_labels);

        uchar* _dataset = new uchar[number_of_labels];
        for(int i = 0; i < number_of_labels; i++) {
            file.read((char*)&_dataset[i], 1);
        }
        return _dataset;
    } else {
        throw runtime_error("Unable to open file `" + full_path + "`!");
    }
}

EDIT: Thanks to @Jürgen Brauer for reminding me to correct my answer, although I have fixed it in my code back in time, but forgot to update the answer.

read_mnist_labels return uchar*, not uchar**

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edit approved May 3, 2016 at 15:40

Community Bot

1
1

uchar**uchar* read_mnist_labels(string full_path, int& number_of_labels) {
    auto reverseInt = [](int i) {
        unsigned char c1, c2, c3, c4;
        c1 = i & 255, c2 = (i >> 8) & 255, c3 = (i >> 16) & 255, c4 = (i >> 24) & 255;
        return ((int)c1 << 24) + ((int)c2 << 16) + ((int)c3 << 8) + c4;
    };

    typedef unsigned char uchar;

    ifstream file(full_path);

    if(file.is_open()) {
        int magic_number = 0;
        file.read((char *)&magic_number, sizeof(magic_number));
        magic_number = reverseInt(magic_number);

        if(magic_number != 2049) throw runtime_error("Invalid MNIST label file!");

        file.read((char *)&number_of_labels, sizeof(number_of_labels)), number_of_labels = reverseInt(number_of_labels);

        uchar* _dataset = new uchar[number_of_labels];
        for(int i = 0; i < number_of_labels; i++) {
            file.read((char*)&_dataset[i], 1);
        }
        return _dataset;
    } else {
        throw runtime_error("Cannot"Unable to open file `" + full_path + "`!");
    }
}

uchar** read_mnist_labels(string full_path, int& number_of_labels) {
    auto reverseInt = [](int i) {
        unsigned char c1, c2, c3, c4;
        c1 = i & 255, c2 = (i >> 8) & 255, c3 = (i >> 16) & 255, c4 = (i >> 24) & 255;
        return ((int)c1 << 24) + ((int)c2 << 16) + ((int)c3 << 8) + c4;
    };

    typedef unsigned char uchar;

    ifstream file(full_path);

    if(file.is_open()) {
        int magic_number = 0;
        file.read((char *)&magic_number, sizeof(magic_number));
        magic_number = reverseInt(magic_number);

        if(magic_number != 2049) throw runtime_error("Invalid MNIST label file!");

        file.read((char *)&number_of_labels, sizeof(number_of_labels)), number_of_labels = reverseInt(number_of_labels);

        uchar* _dataset = new uchar[number_of_labels];
        for(int i = 0; i < number_of_labels; i++) {
            file.read((char*)&_dataset[i], 1);
        }
        return _dataset;
    } else {
        throw runtime_error("Cannot open file `" + full_path + "`!");
    }
}

uchar* read_mnist_labels(string full_path, int& number_of_labels) {
    auto reverseInt = [](int i) {
        unsigned char c1, c2, c3, c4;
        c1 = i & 255, c2 = (i >> 8) & 255, c3 = (i >> 16) & 255, c4 = (i >> 24) & 255;
        return ((int)c1 << 24) + ((int)c2 << 16) + ((int)c3 << 8) + c4;
    };

    typedef unsigned char uchar;

    ifstream file(full_path);

    if(file.is_open()) {
        int magic_number = 0;
        file.read((char *)&magic_number, sizeof(magic_number));
        magic_number = reverseInt(magic_number);

        if(magic_number != 2049) throw runtime_error("Invalid MNIST label file!");

        file.read((char *)&number_of_labels, sizeof(number_of_labels)), number_of_labels = reverseInt(number_of_labels);

        uchar* _dataset = new uchar[number_of_labels];
        for(int i = 0; i < number_of_labels; i++) {
            file.read((char*)&_dataset[i], 1);
        }
        return _dataset;
    } else {
        throw runtime_error("Unable to open file `" + full_path + "`!");
    }
}

deleted 214 characters in body

Source Link

edited Oct 28, 2015 at 7:08

dariush

3.4k
4
29
48

uchar** read_mnist_labels(string full_path, int& number_of_labels, int& label_size) {
    auto reverseInt = [](int i) {
        unsigned char c1, c2, c3, c4;
        c1 = i & 255, c2 = (i >> 8) & 255, c3 = (i >> 16) & 255, c4 = (i >> 24) & 255;
        return ((int)c1 << 24) + ((int)c2 << 16) + ((int)c3 << 8) + c4;
    };

    typedef unsigned char uchar;

    ifstream file(full_path);

    if(file.is_open()) {
        int magic_number = 0;
        file.read((char *)&magic_number, sizeof(magic_number));
        magic_number = reverseInt(magic_number);

        if(magic_number != 2049) throw runtime_error("Invalid MNIST label file!");

        file.read((char *)&number_of_labels, sizeof(number_of_labels)), number_of_labels = reverseInt(number_of_labels);

        label_size = 10;

        uchar**uchar* _dataset = new uchar*[number_of_labels];uchar[number_of_labels];
        for(int i = 0; i < number_of_labels; i++) {
            _dataset[i] = new uchar[label_size];
            memset(_dataset[i], 0, label_size);
            uchar index = 0; file.read((char*)&index&_dataset[i], 1);
            _dataset[i][index] = 1;
        }
        return _dataset;
    } else {
        throw runtime_error("Cannot open file `" + full_path + "`!");
    }
}

uchar** read_mnist_labels(string full_path, int& number_of_labels, int& label_size) {
    auto reverseInt = [](int i) {
        unsigned char c1, c2, c3, c4;
        c1 = i & 255, c2 = (i >> 8) & 255, c3 = (i >> 16) & 255, c4 = (i >> 24) & 255;
        return ((int)c1 << 24) + ((int)c2 << 16) + ((int)c3 << 8) + c4;
    };

    typedef unsigned char uchar;

    ifstream file(full_path);

    if(file.is_open()) {
        int magic_number = 0;
        file.read((char *)&magic_number, sizeof(magic_number));
        magic_number = reverseInt(magic_number);

        if(magic_number != 2049) throw runtime_error("Invalid MNIST label file!");

        file.read((char *)&number_of_labels, sizeof(number_of_labels)), number_of_labels = reverseInt(number_of_labels);

        label_size = 10;

        uchar** _dataset = new uchar*[number_of_labels];
        for(int i = 0; i < number_of_labels; i++) {
            _dataset[i] = new uchar[label_size];
            memset(_dataset[i], 0, label_size);
            uchar index = 0; file.read((char*)&index, 1);
            _dataset[i][index] = 1;
        }
        return _dataset;
    } else {
        throw runtime_error("Cannot open file `" + full_path + "`!");
    }
}

uchar** read_mnist_labels(string full_path, int& number_of_labels) {
    auto reverseInt = [](int i) {
        unsigned char c1, c2, c3, c4;
        c1 = i & 255, c2 = (i >> 8) & 255, c3 = (i >> 16) & 255, c4 = (i >> 24) & 255;
        return ((int)c1 << 24) + ((int)c2 << 16) + ((int)c3 << 8) + c4;
    };

    typedef unsigned char uchar;

    ifstream file(full_path);

    if(file.is_open()) {
        int magic_number = 0;
        file.read((char *)&magic_number, sizeof(magic_number));
        magic_number = reverseInt(magic_number);

        if(magic_number != 2049) throw runtime_error("Invalid MNIST label file!");

        file.read((char *)&number_of_labels, sizeof(number_of_labels)), number_of_labels = reverseInt(number_of_labels);

        uchar* _dataset = new uchar[number_of_labels];
        for(int i = 0; i < number_of_labels; i++) {
            file.read((char*)&_dataset[i], 1);
        }
        return _dataset;
    } else {
        throw runtime_error("Cannot open file `" + full_path + "`!");
    }
}

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answered Oct 28, 2015 at 7:02

dariush

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