建造者模式用于分离复杂对象的构建和表示，使得同样的构建过程可以创建不同的表示。在c++中，当一个类的构造函数参数过多，或者对象的构建步骤较复杂、存在多种变体时，使用建造者模式能显著提升代码可读性和可维护性。
建造者模式的核心思想
将对象的构建逻辑从构造函数中剥离出来，通过一个独立的Builder类逐步配置和组装对象。最终通过build()方法生成目标对象。这种方式避免了“伸缩构造器反模式”（telescoping constructors），即写多个参数不同的构造函数。
比如我们要构建一个复杂的Computer类，包含CPU、内存、硬盘、显卡等组件，不同配置组合多样。
基本实现结构
定义产品类、抽象建造者、具体建造者和指挥者（可选）。
示例代码：
#include <iostream> #include <string> // 1. 产品类：Computer class Computer { public: void setCPU(const std::string& cpu) { m_cpu = cpu; } void setRAM(const std::string& ram) { m_ram = ram; } void setStorage(const std::string& storage) { m_storage = storage; } void setGPU(const std::string& gpu) { m_gpu = gpu; } void show() const { std::cout << "Computer Config:n"; std::cout << " CPU: " << m_cpu << "n"; std::cout << " RAM: " << m_ram << "n"; std::cout << " Storage: " << m_storage << "n"; std::cout << " GPU: " << m_gpu << "n"; } private: std::string m_cpu; std::string m_ram; std::string m_storage; std::string m_gpu; }; // 2. 抽象建造者 class ComputerBuilder { public: virtual ~ComputerBuilder() = default; virtual void buildCPU() = 0; virtual void buildRAM() = 0; virtual void buildStorage() = 0; virtual void buildGPU() = 0; virtual Computer* getComputer() = 0; }; // 3. 具体建造者：游戏电脑 class GamingComputerBuilder : public ComputerBuilder { public: GamingComputerBuilder() { m_computer = new Computer(); } void buildCPU() override { m_computer->setCPU("Intel i9"); } void buildRAM() override { m_computer->setRAM("32GB DDR5"); } void buildStorage() override { m_computer->setStorage("1TB NVMe SSD"); } void buildGPU() override { m_computer->setGPU("RTX 4090"); } Computer* getComputer() override { Computer* temp = m_computer; m_computer = nullptr; return temp; } ~GamingComputerBuilder() { delete m_computer; } private: Computer* m_computer; }; // 4. 具体建造者：办公电脑 class officeComputerBuilder : public ComputerBuilder { public: OfficeComputerBuilder() { m_computer = new Computer(); } void buildCPU() override { m_computer->setCPU("Intel i5"); } void buildRAM() override { m_computer->setRAM("16GB DDR4"); } void buildStorage() override { m_computer->setStorage("512GB SATA SSD"); } void buildGPU() override { m_computer->setGPU("Integrated Graphics"); } Computer* getComputer() override { Computer* temp = m_computer; m_computer = nullptr; return temp; } ~OfficeComputerBuilder() { delete m_computer; } private: Computer* m_computer; }; // 5. 指挥者（可选） class Director { public: void setBuilder(ComputerBuilder* builder) { m_builder = builder; } Computer* construct() { m_builder->buildCPU(); m_builder->buildRAM(); m_builder->buildStorage(); m_builder->buildGPU(); return m_builder->getComputer(); } private: ComputerBuilder* m_builder; };使用方式
通过Director控制构建流程，或直接调用Builder的各个步骤。
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int main() { Director director; GamingComputerBuilder gamingBuilder; OfficeComputerBuilder officeBuilder; // 构建游戏电脑 director.setBuilder(&gamingBuilder); Computer* gamingPC = director.construct(); gamingPC->show(); std::cout << "n"; // 构建办公电脑 director.setBuilder(&officeBuilder); Computer* officePC = director.construct(); officePC->show(); delete gamingPC; delete officePC; return 0; }现代C++中的流式建造者（Fluent Builder）
更符合C++习惯的方式是使用链式调用，提升API易用性。
class Computer { public: Computer& cpu(const std::string& c) { m_cpu = c; return *this; } Computer& ram(const std::string& r) { m_ram = r; return *this; } Computer& storage(const std::string& s) { m_storage = s; return *this; } Computer& gpu(const std::string& g) { m_gpu = g; return *this; } void show() const { std::cout << "Custom Computer:n"; std::cout << " CPU: " << m_cpu << "n"; std::cout << " RAM: " << m_ram << "n"; std::cout << " Storage: " << m_storage << "n"; std::cout << " GPU: " << m_gpu << "n"; } private: std::string m_cpu; std::string m_ram; std::string m_storage; std::string m_gpu; }; // 使用示例 /* Computer myPC; myPC.cpu("amd Ryzen 7") .ram("32GB") .storage("2TB SSD") .gpu("RTX 4070") .show(); */这种风格简洁直观，适合配置类对象，广泛应用于现代C++库设计中。