C + + Programming attention issues __linux

1, when the string type is initialized with two iterators, such as String str (Str1.begin (), Str1.begin () +5), in fact, the above is an interval open after the opening, that is to say, Str1,begin () + 5 The characters pointed to are not copied.

2, void * memset (void * ptr, int value, size_t num); initializes the first Num area pointed to by PTR with value, an initialization method.

3, to determine whether two floating-point types of variables are equal do not use a==b form, but should determine the difference between the absolute value of two numbers is less than a threshold.

It is not correct to compare floating-point data types directly using the operator = =, <=, >=,!=, and so on in your code. The correct approach should be to compare the difference or the decimal.

4, array pointer and array of pointers silly to know: int *p[], first you need to understand [] the priority is higher than *,p first and [] combined, indicating that it is an array, and * union, indicating that the variables in the array are pointers; int (*p) [],p First and *, so p is a pointer, and [] combines , which indicates that the pointer points to an array.

5, the string, the first use string, encountered a variable array, the use of vector first, you can use STL don't write yourself.

6, size_t type use special attention, it cannot be negative, so do not commit size_t T;while (t>=0) {--t}; Such a mistake, because t can never be negative.

7, to determine whether an integer is odd, with x%2!=0, do not use x%2==1, because x may also be negative.

8, after using the new must use Delete, they and (), {},[] like, are in pairs appear.

9, if (t), while (t), and so on, the following omitted are "!=0/null"; True 1,false is 0;a==b this form, equal (true) returns 1, unequal (for false) returns 0;

10, STL Standard Template Library is a part of C + + standard library, C + + standard library and HP,SGI, such as the implementation of STL version, the most of the STL Standard Template Library is implemented in the SGI; however, in the use of so much, the STL standard library header file is not an extension of the name, Directly include the relevant header file; STL has a lot of practical algorithms, familiar with its use can save a lot of time, and STL implementation of the version of the performance will not be worse than their own write to where.

11, Private: Only by 1. The function in this class, 2. Its friend function access. cannot be accessed by any other object, nor can objects of that class be accessed. Protected: can be accessed by 1. Functions in the class, 2. Subclass functions, and 3. Its friend function access. But cannot be accessed by objects of this class.  Public: can be accessed by 1 functions in the class, functions in 2. Subclasses, 3. Its friend function, or by 4. The object of the class. Note: The friend function includes 3 kinds: a normal, non-member function that is set as a friend, a member function of another class that is set as a friend, and is set to all member functions in a friend class.