Please tell me what the single semicolon is used for in these examples.

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C++

Please tell me what the single Semicolon is used for in these 2 examples.
Example 1:

Super(const std::string& str) : mStr(str) {}

Example 2:

Sub(int i) : Super(""), mInt(i) {}

class Super {  
public:  
Super(const std::string& str) : mStr(str) {}
private: std::string mStr;  };

Class Sub : public Super {  
public:
 using Super::Super;
Sub(int i) : Super(""), mInt(i) {}
private int mInt;  };

What I have tried:

Please tell me what the single Semicolon is used for in these 2 examples.
Example 1: Super(const std::string& str) : mStr(str) {}
Example 2: Sub(int i) : Super(""), mInt(i) {}



class Super {
public:
Super(const std::string& str) : mStr(str) {}
private: std::string mStr; };

Class Sub : public Super {
public:
using Super::Super;
Sub(int i) : Super(""), mInt(i) {}
private int mInt; };