Conversion between C++ string types and numbers

Conversion between C++ string types and numbers

Reprinted: http://www.cnblogs.com/luxiaoxun/archive/2012/08/03/2621803.html

1. Conversion between string numbers

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

Character array---string
(2)char * -->string
   char *p = "OK";
   string str(p);

Character array---CString
(3)char * -->CString 
   char *p ="OK";
   CString m_Str(p);
   //or
   CString m_Str;
   m_Str.Format("%s",p);

CString---Character array
(4) CString --> char *
   CString str("OK");
   char * p = str.GetBuffer(0);
   ...
   str.ReleaseBuffer();

(5)string --> CString  
   CString.Format("%s", string.c_str());  

(6)CString --> string
   string s(CString.GetBuffer(0));  
   Be sure to ReleaseBuffer after GetBuffer() (), otherwise the space occupied by the buffer is not released, and the CString object cannot grow dynamically.

(7)double/float->CString
   double data;
   CString.Format("%.2f",data); //Keep 2 decimal places

(8) CString->double
   CString s="123.12";
   double d=atof( s);   
 
(9)string->double
  double d=atof(s.c_str());

2. Number to string: use sprintf() function
string formatting command, the main function is to write formatted data In a string.

Function prototype

int sprintf( char *buffer, const char *format, [ argument] … );

parameter list

buffer: char pointer, pointing to the buffer of the string to be written.

format: format string.

[argument]...: Optional parameters, which can be any type of data.

return value

String length (strlen)

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 hexadecimal is converted to hexadecimal, if the output uppercase letter is sprintf(str,"%X",a)
------------ --------
char *itoa(int value, char* string, int radix); 
also can convert numbers to strings, but the function itoa() is platform-dependent (not in the standard), so It is not recommended to use this function here.

3. Convert a string to a number: use the sscanf() function
to read data that matches the specified format from a string.

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); // Hexadecimal is converted to decimal.

In addition, atoi(), atol(), atof() can also be used.

4. Use stringstream class

Use ostringstream object to write a string, similar to sprintf() 
  ostringstream s1;
  int i = 22;
  s1 << "Hello "<< i << endl;
  string s2 = s1.str();
  cout << s2;

read a string with the isringstream object, similar to sscanf() 
  istringstream stream1;
  string string1 = "25";
  stream1.str(string1);
  int i;
  stream1 >> i;
  cout << i << endl;  // displays 25

Writing code is an art, better than Mona Lisa's smile.

Category:  C++ basic concepts