Conversion of numbers to strings in C + + scanf string Summary (review required)

1 scanf read-in operation of string

C + + inside the console input directly using the CIN operation can be, or getline (istringstream,string);.

Only built-in type Int,float,char,double,bool can be assigned directly, scanf read into string cannot be directly assigned using SCANF, because string is a class, has a special initialization function, cannot use scanf, It is also a char pointer that is received by the same token. The same is true of sizeof, a programming language, that cannot be manipulated directly on a string.

string s;s.resize (+); scanf ("%s", &s[0]);

Or:

string s; Char New Char (scanf); ("%s", c); // scanf ("%s", &c[0]); s = c;//to the first address

Strlen is a valid string to get input, instead of opening the space size to 100.

What Strlen does is work on a counter that starts scanning from somewhere in memory (which can be the beginning of a string, somewhere in the middle, or even an indeterminate area of memory) until it touches the first string Terminator , and then returns the counter value. --means the actual length of the actual string or array of characters (not the number of bytes in the occupied space).

 char a[6]={' a ', ' B ', ' n ', ' d ', ' e ', ' R '};  
 int I=strlen (A);           //i for 2, because to  0 ' End, so the actual a[] only  sizeof ()      

 string   S;  char  *c = new  char  (100    " %s   " ,c);  int  len = strlen (c); S1.resize (len);// Dynamically compiled S1.assign (c,c  + len); // copy (C,c + len,s1.begin ());     

 class x  
 {  
 int i;  
 
      
       int j;  
       
 
       char k;  
 };  
 x x;  
    
          < Span lang= "en-US" >cout<<sizeof (X) <<endl;  results  12 = = = Memory   
 cout<<sizeof (x) <<endl;  results  12  ibid.   
 class X, the largest space occupied by the members is int type of space  4 bytes, so memory is filled, the final result is  ((int) (actual member occupied memory space and /4) +1) * *   

* So you cannot get the actual number of char elements by sizeof (string)/sizeof (string[0]), regardless of the number of strings, the final result is 28, because string is a class.

Copy () Usage:

This algorithm receives three iterator iterator, the first two representing an input range, and the third represents the starting position of the destination sequence.

Conversions of Char and int:

int = char-' 0 ';

char = int + ' 0 ';

2 conversion between numbers and strings in C + + (important)

1. Conversion between string numbers

(1) string---char *
String str ("OK");
Const char * p = str.c_str ();

(2) char *-->string
Char *p = "OK";
String str (p);
(3) String->double
Double D=atof (S.c_str ());

Common functions Atoi (), itoa (), to_string ();

2. Numeric to String: Use sprintf () function

Char str[10];
int a=1234321;
sprintf (str, "%d", a);
--------------------
Char str[10];
Double a=123.321;
sprintf (str, "%.3LF", a);
--------------------
Char str[10];
int a=175;
sprintf (str, "%x", a),//10 conversion into 16, if the output uppercase letter is sprintf (str, "%x", a)
--------------------
char *itoa (int value, char* string, int radix);
It is also possible to convert a number to a string, but itoa () is a platform-dependent (not standard) function, so it is not recommended here.

3. String to number: using the sscanf () function

Char str[]= "1234321";
int A;
SSCANF (str, "%d", &a);
.............
Char str[]= "123.321";
Double A;
SSCANF (str, "%LF", &a);
.............
Char str[]= "AF";
int A;
SSCANF (str, "%x", &a); 16 binary converted to 10 binary

Alternatively, you can use Atoi (), Atol (), Atof ().

4. Using StringStream class

Write a string with the Ostringstream object, similar to sprintf ()
Ostringstream S1;
int i = 22;
S1 << "Hello" << i << Endl;
String s2 = S1.str ();
cout << S2;

Reads a string with the Istringstream object, similar to SSCANF ()
Istringstream stream1;
String string1 = "25";
STREAM1.STR (string1);
int i;
Stream1 >> i;
cout << i << Endl; Displays 25

3 Summary of all function operations of the string class

append ()		&nbs P;

Conversion of numbers to strings in C + + scanf string Summary (review required)