There's no escaping the pit. Default parameters for--c++ functions (redefine default parameters)

The default parameter refers to the automatic use of a value when an argument is omitted from a function call.

The first thing to note here is:
for a function with a parameter list, you must add a default value from right to left.
That is, to set a default value for a parameter, you must provide a default value for all parameters to the right of it.

The pit that I met today is that the function uses the default parameters, and the declaration and definition of the function are separate.

char* left(constcharstrint n=1);int main(){}char* left(constcharstrint1)//错误{}

The above code can be modified in two ways:

1 declaration with default parameters, no default value when implemented

char* left(constcharstrint n=1);int main(){}char* left(constcharstrint n ){}

2 implemented with default parameters, no default value declared

char* left(constcharstrint n);int main(){}char* left(constcharstrint1){}

There is a mistake that we often make.
In many cases, we can use default parameters instead of function overloads:

void point(int，int){//...}void point(int a){return point(a，4)；}void point(){return point(3，4)；}

You can use the following function to override the default parameters:

void point(int=3,int=4)；

Called Point (3,4) when a "point ();" is called, which is the 3rd overloaded function declared.
When a "point (6);" is called, it is called "point (6,4);", which is the 2nd overloaded function declared.
An overloaded function that calls the 1th declaration when "Point (7,8);" is called

When you are happy, if a set of overloaded functions (which may have default parameters) allows the same number of calls, it will cause the two semantics of the call.
　　　　

func(int//重载函数之一func(int，int=4//重载函数之二，带有默认参数func(int=3，int=4//重载函数之三，带有默认参数func(7//error: 到底调用3个重载函数中的哪个?func(20,30//error：到底调用后面2个重载函数的哪个?

There's no escaping the pit. Default parameters for--c++ functions (redefine default parameters)