C++字符串轉數字,數字轉字符串

1. 字符串轉數字

如將“32”轉為32，將“3.1415”轉為3.1415，將“567283”轉為567283。使用：

//Convert string to integer, more @http://www.cplusplus.com/reference/clibrary/cstdlib/atoi/
int atoi ( const char * str );
//Convert string to double, more @http://www.cplusplus.com/reference/clibrary/cstdlib/atof/
double atof ( const char * str ); 
// Convert string to long integer,more @http://www.cplusplus.com/reference/clibrary/cstdlib/atol/
long int atol ( const char * str );  
//Read formatted data from string, more @http://www.cplusplus.com/reference/clibrary/cstdio/sscanf/
int sscanf ( const char * str, const char * format, ...);

Example1:

/* atoi,atof,atol example */
#include <stdio.h>
#include <stdlib.h>
int main ()
{
  int a;float b;long c;
  a=atoi("32");
  b=atof("3.1415");
  c=atol("567283");
  printf ("%d,%f,%d",a,b,c); 
  return 0;
}

Output:
32,3.141500,567283

Example2:

/* sscanf example */
#include <stdio.h>
int main ()
{
  int a;float b;long c;
  sscanf ("32,3.1415,567283","%d,%f,%d",&a,&b,&c);
  printf ("%d,%f,%d",a,b,c);   
  return 0;
}

Output:
32,3.141500,567283

2. 數字轉字符串

如將32轉為“32”，將3.1415轉為“3.1415”，將567283轉為“567283”。使用：

//Write formatted data to string, more @http://www.cplusplus.com/reference/clibrary/cstdio/sprintf/
int sprintf ( char * str, const char * format, ... );
//Convert integer to string (non-standard function), more @http://www.cplusplus.com/reference/clibrary/cstdlib/itoa/
//This function is not defined in ANSI-C and is not part of C++, but is supported by some compilers.
//A standard-compliant alternative for some cases may be sprintf.
char *  itoa ( int value, char * str, int base );

Example3:

Example3

/* sprintf example */
#include <stdio.h>
int main ()
{
  char a[10],b[10],c[10];
  sprintf(a, "%d", 32);
  sprintf(b, "%f", 3.1415);
  sprintf(c, "%d", 567283);
  printf("%s,%s,%s",a,b,c);
  return 0;
}

Output:
32,3.141500,567283

3. 使用stringstream進行字符串與數字的轉換

這里給出一個例子，更多 @http://www.cppblog.com/Sandywin/archive/2008/08/27/27984.html，http://blog.csdn.net/touzani/article/details/1623850

Example4:

Example4

// using stringstream constructors.
#include <iostream>
#include <sstream>
using namespace std;
int main () 
{
  int a;float b;long c;
  char d[10],e[10],f[10];

  /* string to number */
  stringstream ss;
  ss << "32";
  ss >> a;
  ss.clear();

  ss << "3.1415";
  ss >> b;
  ss.clear();

  ss << "567283";
  ss >> c;
  ss.clear();

  cout<<a<<","<<b<<","<<c<<endl;

  /* number to string */
  ss << a;
  ss >> d;
  ss.clear();

  ss << b;
  ss >> e;
  ss.clear();

  ss << c;
  ss >> f;
  ss.clear();

  cout<<d<<","<<e<<","<<f<<endl;

  return 0;
}

Output:
32,3.141500,567283
32,3.141500,567283

小結：C++標准庫中的<sstream>提供了比ANSI C的<stdio.h>更高級的一些功能，即單純性、類型安全和可擴展性，可以使用這些庫來實現安全和自動的類型轉換。言下之意就是，使用stringstream進行字符串與數字的轉換是更好的選擇。