泛型编程
写一个交换函数，在学习模板之前，为了匹配不同的参数类型，我们可以利用函数重载来实现。
代码语言：javascript
AI代码解释
void Swap(int& a, int& b) { int c = a; a = b; b = c; } void Swap(char& a, char& b) { char c = a; a = b; b = c; } void Swap(double& a, double& b) { double c = a; a = b; b = c; } //...虽然这样似乎解决了问题，但是这样的设计写着太过麻烦，只要出现新类型就需要写新的函数，代码的复用率很低。有没有什么可以让我们一劳永逸呢？模板就可以实现这一功能。
这种通过抽象和模板化来编写可重用和灵活的代码以此提升代码的可读性和维护性，同时避免代码重复的方式称为泛型编程。
函数模板
函数模板是c++中的一类机制，通过在函数定义中使用模板参数，我们可以编写一个函数，而在调用时根据实际参数的类型自动生成相应的版本。
代码语言：javascript
AI代码解释
template <class T> void Swap(T& a, T& b) { T c = a; a = b; b = c; }这样编译器就可以根据传入的参数类型来生成对应的Swap()函数，大大提高了代码的复用率。下面我们来尝试运行一下。
代码语言：javascript
AI代码解释
template <class T> void Swap(T& a, T& b) { T c = a; a = b; b = c; } int main() { int a,b; a = 1; b = 2; double c, d; c = 0.0; d = 1.2; Swap(a, b); Swap(c, d); cout << a << " " << b << endl; cout << c << " " << d << endl; return 0; }我们发现，调用Swap()之后，int类型的ab和double类型的cd都完成了交换。但是他们是否调的是同一个函数呢？
转到反汇编：
我们发现两次调用的是不同的Swap()函数，根据传入参数类型的不同 ，编译器会生成不同的函数。然后再调用生成的函数。
函数模板的实例化
通过函数模板生成对应函数的过程叫做函数实例化。
当模板的参数只有一个时，却传入了不同类型的变量，编译器无法推导出T的类型，出现了推导错误
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