C ++ learning [1]

String

1.Several Special Data Types

 

String S ("hello ");
S. Size () = 6 string: size_type (unsigned type)

 

 

Int * P1, * P2;
Ptrdiff_t n = p1-P2; // pointer difference
# Include <cstddef>
Ptrdiff_t (signed INT)

 

 

Vector subscript type: size_type

String subscript type string: size_type

Array subscript type size_t

 

2. String and array

String S1, S2 = "hello ";
S1 = S2; // a string can be directly assigned a value.
Int Ia [] = {0, 1, 2 };
Int ia2 [3];
Ia2 = IA; // array is not allowed

 

 

3. Dynamic Array

Size_t n = get_size (); // The value is available only when an empty array get_size () is dynamically allocated.
Int * P = new int [ N];
 
String * PSA = new string [10]; // string is not of the built-in type. Memory is allocated and elements are initialized.
Int * Pia = new int [10]; // Int Is of the built-in type, memory is allocated, and elements are not initialized (so the const type is incorrect)
Int * Pia = new int [10] (); // force the compiler to initialize

 

 

4. cStyle string

# Include <cstdlib>
Int * Pi = NULL; // null is the C style

 

 

# Incldue <cstring>
Strlen (s) strcmp (S1, S2 )....
Char Ca [] = {'C', '+', '+ '};
Strlen (CA); // dangerous strlen judge the end based on the string Terminator null

 

 

5. Const and pointer

C ++ requires that the pointer to the const object must also have the const feature, but allows the address of a non-const object to be assigned to the pointer to the const object.

Const double Pi = 3.14;
Double * PTR = & PI; // Error
 
Double dval = 3.14;
Const double * cptr;
Cptr = & dval // correct, so the const pointer can point to the object value.

 

6. Differences in auto-increment operations

I ++; // you need to save the original I value.
++ I; // do less work

 

 

Vector <int> ivec;
Int CNT = 10;
While (CNT> 0)
Ivec. pust_back (CNT --);
Vector <int>: iterator iter = ivec. Begin ();
While (ITER! = Ivec. End ())
Cout <* ITER ++ <Endl; // * ITER ++ (ITER ++)

 

 

7. Arrow operators->

C ++ is the synonym used after the dot operator to dereference the operation definition.

(* P). Foo; óp-> Foo;

 

8. sizeof Operator

The sizeof operation on an array is equivalent to the sizeof operation on its element type. The result is multiplied by the number of array elements.

Int SZ = sizeof (IA)/sizeof (* IA); // obtain the number of array elements