C 编程思想 答案 第七章 其他章节请点击用户名找 thinking in C annotated solution guide(charpter 7).docVIP

[ ] [ ] [ ] [ ] [ ] [ ] Annotated Solution Guide Revision 1.0 for Thinking in C++, 2nd edition, Volume 1 by Chuck Allison ?2001 MindView, Inc. All Rights Reserved. [ ] [ ] [ ] Chapter 7 7-1 Create a Text class that contains a string object to hold the text of a file. Give it two constructors: a default constructor and a constructor that takes a string argument that is the name of the file to open. When the second constructor is used, open the file and read the contents into the string member object. Add a member function contents( ) to return the string so (for example) it can be printed. In main( ), open a file using Text and print the contents. Solution: //: S07:Text.cpp #include lt;iostreamgt; #include lt;fstreamgt; #include lt;stringgt; using namespace std; class Text { string text; public: Text() {} Text(const stringamp; fname) { ifstream ifs(fname.c_str()); string line; while (getline(ifs, line)) text += line + ‘\n’; } string contents() { return text; } }; int main(int argc, char* argv[]) { if (argc gt; 1) { Text t1; Text t2(argv[1]); cout lt;lt; quot;t1 :\nquot; lt;lt; t1.contents() lt;lt; endl; cout lt;lt; quot;t2 :\nquot; lt;lt; t2.contents() lt;lt; endl; } } ///:~ When creating a Text object, the compiler guarantees that the text data member has its default constructor (string::string( )) executed before either Text constructor runs, hence the default Text constructor just builds an empty string. This program prints an empty string for t1 followed by the contents of the file named in the first command-line argument. Note the use of string::c_str( ) in the second constructor. That’s because the ifstream constructor takes a char* argument, not a string. 7-2 Create a Message class with a constructor that takes a single string with a default value. Create a private member string, and in the constructor simply assign the argument string to your internal string. Create two overloaded member functions call