C++primer Chapter III

//1. Code that is located in a header file should not generally use a using declaration. This is because the contents of the header file are copied to all the files that reference it, which can result in unexpected namespace collisions. //three ways to use names in namespaces    using namespaceStd//It is best not to use in the header file, it is easy to cause namespace name pollution, resulting in naming conflicts    usingSTD::string; STD::string;//2. A set of functions for manipulating characters is defined in the header file Cctype//isalnum (), Isalpha (), Iscntrl (), IsDigit (), Isgraph (), Isprint (), ispunct (), Isspace (), Isupper (), Isxdigit (), Tolow ER (), toupper ()//3. For operator &&, only the left evaluates to true to continue evaluating the right side//4. When it is unclear what type of container to use, use an iterator to manipulate the elements of the container and use the actions common to the iterator (*it, It->men, ++it,--it, it1 = = It2, it1! = it2), which is convenient when replacing the container. vector<int> Vecint (Ten);//10 0 is stored in the Vecint, the value is initialized at this timevector<int>::iterator Itvec =Vecint.begin ();//5. The number of elements in an array is also part of the array type, and the compile-time dimension should be known, so its dimension must be a constant expression.     Charbuff[Ten] ="SZN";//allows the use of a string constant to initialize the character array buff is readable and writable    Char*str ="SZN";//It's best not to use it    /*string Constants in C++03 const CHAR[N] When there is an obvious target type, the result of a conversion as a qualifying modification is char*, which is an obsolete clause that has been discarded in c++11, that is, in c++03, Char *tem= "    Szn "; Is legal but illegal in c++11, c++11 must write this: const char * tem =" SZN "; In C, a sequence of characters enclosed in double quotation marks is not called a string constant, it is just a string literal, and C's string literal is not a constant, because C's constants and constant expressions are only compile-time.    string literals in C + + can be called string constants.    The string literal type in C is char[n], the array-to-pointer conversion result is char*, and the string constant type in C + + is const CHAR[N], and the result of the array-to-pointer conversion is the const char*. *///6. An attribute of an array: In many places where the array name is used, the compiler automatically replaces it with a pointer to the first element of the array, and the pointer loses the attributes of all the arrays. //The new 7.C++11 Standard introduces two functions called Begin (), End (), and is similar to the container's function of the same name. Can be used for built-in arrays. defined in the header file iterator. //8. The value in the subscript operator for the built-in type can be negative, but the standard library type qualifies the subscript that it uses to be an unsigned type. 

C++primer Chapter III