结构体 #

% 创建结构体
student.name = '张三';
student.age = 20;
student.scores = [85 90 78];

% 查看结构体
student
% student = 
%     name: '张三'
%      age: 20
%   scores: [85 90 78]

% 逐字段赋值
person.name = '李四';
person.age = 25;
person.city = '北京';

% 添加新字段
person.email = 'lisi@example.com';

% 使用struct函数创建
student = struct('name', '王五', ...
                 'age', 22, ...
                 'major', '计算机');

% 创建空结构体
empty_struct = struct();

% 创建带空字段的结构体
s = struct('a', {}, 'b', {});

% 创建结构体数组
students(1).name = '张三';
students(1).age = 20;
students(2).name = '李四';
students(2).age = 22;

% 使用struct创建
students = struct('name', {'张三', '李四'}, ...
                  'age', {20, 22});

student.name = '张三';
student.age = 20;
student.scores = [85 90 78];

% 点号访问
name = student.name;        % '张三'
age = student.age;          % 20
scores = student.scores;    % [85 90 78]

% 动态字段名
field = 'name';
value = student.(field);    % '张三'

% 创建结构体数组
students(1).name = '张三';
students(1).age = 20;
students(2).name = '李四';
students(2).age = 22;
students(3).name = '王五';
students(3).age = 21;

% 访问单个元素
name1 = students(1).name;   % '张三'

% 访问所有元素的某字段
names = {students.name};    % {'张三', '李四', '王五'}
ages = [students.age];      % [20 22 21]

% 嵌套结构体
university.name = '清华大学';
university.location.city = '北京';
university.location.province = '北京';
university.students.undergrad = 15000;
university.students.graduate = 20000;

% 访问嵌套字段
city = university.location.city;        % '北京'
grad_count = university.students.graduate;  % 20000

student.name = '张三';

% 直接添加
student.age = 20;
student.scores = [85 90 78];

% 使用setfield
student = setfield(student, 'email', 'zhangsan@example.com');

student.name = '张三';
student.age = 20;
student.temp = '临时数据';

% 删除单个字段
student = rmfield(student, 'temp');

% 删除多个字段
student = rmfield(student, {'age', 'email'});

% 保留指定字段
student = keepfield(student, {'name', 'scores'});

student.name = '张三';
student.age = 20;

% 直接修改
student.age = 21;

% 使用setfield
student = setfield(student, 'name', '李四');

student.name = '张三';
student.age = 20;

% 使用struct重命名
student = struct('姓名', student.name, '年龄', student.age);

% 或手动处理
new_student.姓名 = student.name;
new_student.年龄 = student.age;
student = new_student;

student.name = '张三';
student.age = 20;
student.scores = [85 90 78];

% 获取所有字段名
fields = fieldnames(student);
% {'name'; 'age'; 'scores'}

% 检查字段是否存在
has_name = isfield(student, 'name');    % true
has_email = isfield(student, 'email');  % false

% 获取字段值
age = getfield(student, 'age');         % 20

% 判断是否为结构体
isstruct(student)    % true

% 结构体数组大小
students(1).name = '张三';
students(2).name = '李四';
size(students)       % [1, 2]

% 字段数量
n = numel(fieldnames(student));  % 3

% 结构体数组转表
students(1).name = '张三';
students(1).age = 20;
students(2).name = '李四';
students(2).age = 22;

T = struct2table(students);
% name    age
% ____    ___
% '张三'  20 
% '李四'  22 

% 表转结构体数组
S = table2struct(T);

student.name = '张三';
student.age = 20;

% 结构体转元胞数组
c = struct2cell(student);
% {'张三'; 20}

% 元胞数组转结构体
fields = {'name', 'age'};
values = {'李四', 22};
s = cell2struct(values, fields, 2);

% 方法1：逐个赋值
students(1).name = '张三';
students(1).age = 20;
students(2).name = '李四';
students(2).age = 22;

% 方法2：使用struct
students = struct('name', {'张三', '李四', '王五'}, ...
                  'age', {20, 22, 21});

% 方法3：使用repmat
student = struct('name', '默认', 'age', 0);
students = repmat(student, 3, 1);

students(1).name = '张三';
students(1).scores = [85 90];
students(2).name = '李四';
students(2).scores = [78 88];
students(3).name = '王五';
students(3).scores = [92 95];

% 提取所有name
names = {students.name};    % {'张三', '李四', '王五'}

% 提取所有scores
all_scores = cat(1, students.scores);
% [85 90; 78 88; 92 95]

% 计算平均分
avg_scores = mean(all_scores, 2);

students(1).name = '张三';
students(1).age = 20;
students(2).name = '李四';
students(2).age = 22;
students(3).name = '王五';
students(3).age = 21;

% 筛选年龄大于20的学生
ages = [students.age];
mask = ages > 20;
older_students = students(mask);

% 创建学生结构体
function student = createStudent(name, age, scores)
    student.name = name;
    student.age = age;
    student.scores = scores;
    student.average = mean(scores);
    student.grade = getGrade(student.average);
end

function g = getGrade(avg)
    if avg >= 90
        g = 'A';
    elseif avg >= 80
        g = 'B';
    elseif avg >= 70
        g = 'C';
    elseif avg >= 60
        g = 'D';
    else
        g = 'F';
    end
end

% 使用
student1 = createStudent('张三', 20, [85 90 78]);
student2 = createStudent('李四', 22, [92 88 95]);

% 创建配置结构体
config.database.host = 'localhost';
config.database.port = 3306;
config.database.name = 'mydb';
config.database.user = 'root';

config.logging.level = 'INFO';
config.logging.file = 'app.log';

config.app.name = 'MyApp';
config.app.version = '1.0.0';

% 使用配置
function conn = connect(config)
    fprintf('连接到 %s:%d/%s\n', ...
            config.database.host, ...
            config.database.port, ...
            config.database.name);
end

% 存储实验结果
experiment.name = '温度测试';
experiment.date = '2024-03-27';
experiment.parameters.temperature = [25 50 75 100];
experiment.parameters.pressure = 1.0;
experiment.results.measurements = rand(4, 10);
experiment.results.mean = mean(experiment.results.measurements, 2);
experiment.results.std = std(experiment.results.measurements, 0, 2);

% 保存到文件
save('experiment.mat', 'experiment');

% 使用结构体
student.name = '张三';
student.age = 20;
student.scores = [85 90];
student.average = mean(student.scores);

% 使用类（更复杂但更规范）
classdef Student
    properties
        name
        age
        scores
    end
    methods
        function obj = Student(name, age, scores)
            obj.name = name;
            obj.age = age;
            obj.scores = scores;
        end
        function avg = getAverage(obj)
            avg = mean(obj.scores);
        end
    end
end

% 推荐：使用小写和下划线
student.student_name = '张三';
student.student_id = '001';

% 不推荐：使用驼峰或特殊字符
student.studentName = '张三';  % 可行但不推荐

% 不推荐：动态扩展
for i = 1:1000
    data(i).value = rand();
end

% 推荐：预分配
data = struct('value', cell(1, 1000));
for i = 1:1000
    data(i).value = rand();
end

% 动态访问字段
fields = {'name', 'age', 'scores'};
student.name = '张三';
student.age = 20;
student.scores = [85 90];

for i = 1:length(fields)
    field = fields{i};
    fprintf('%s: ', field);
    disp(student.(field));
end