/in/foo.cc: In function 'void replaceAll(std::string&, const std::string&, const std::string&)':
/in/foo.cc:8:35: warning: comparison of integer expressions of different signedness: 'long long int' and 'const std::__cxx11::basic_string<char>::size_type' {aka 'const long unsigned int'} [-Wsign-compare]
    8 |         while((i=str.find(from,i))!=string::npos)  //npos为字符串的末尾
      |               ~~~~~~~~~~~~~~~~~~~~^~~~~~~~~~~~~~