Celebrate National IT Professionals Day with 3 months of free Premium Membership. Use Code ITDAY17

x
?
Solved

Convert String to Integer

Posted on 2004-10-07
5
Medium Priority
?
94,384 Views
Last Modified: 2011-08-18
How can I convert a standard string to an integer?
0
Comment
Question by:rossryan
[X]
Welcome to Experts Exchange

Add your voice to the tech community where 5M+ people just like you are talking about what matters.

  • Help others & share knowledge
  • Earn cash & points
  • Learn & ask questions
  • 2
  • 2
5 Comments
 
LVL 86

Expert Comment

by:jkr
ID: 12251838
There are several methods, the easiest being 'atoi()' the most flexible IMHO (in terms of error checking) being 'strtol()':


/* ATOF.C: This program shows how numbers stored
 * as strings can be converted to numeric values
 * using the atof, atoi, and atol functions.
 */

#include <stdlib.h>
#include <stdio.h>

void main( void )
{
   char *s; double x; int i; long l;

   s = "  -2309.12E-15";    /* Test of atof */
   x = atof( s );
   printf( "atof test: ASCII string: %s\tfloat:  %e\n", s, x );

   s = "7.8912654773d210";  /* Test of atof */
   x = atof( s );
   printf( "atof test: ASCII string: %s\tfloat:  %e\n", s, x );

   s = "  -9885 pigs";      /* Test of atoi */
   i = atoi( s );
   printf( "atoi test: ASCII string: %s\t\tinteger: %d\n", s, i );

   s = "98854 dollars";     /* Test of atol */
   l = atol( s );
   printf( "atol test: ASCII string: %s\t\tlong: %ld\n", s, l );
}

Output

atof test: ASCII string:   -2309.12E-15   float:  -2.309120e-012
atof test: ASCII string: 7.8912654773d210   float:  7.891265e+210
atoi test: ASCII string:   -9885 pigs      integer: -9885
atol test: ASCII string: 98854 dollars      long: 98854

/* STRTOD.C: This program uses strtod to convert a
 * string to a double-precision value; strtol to
 * convert a string to long integer values; and strtoul
 * to convert a string to unsigned long-integer values.
 */

#include <stdlib.h>
#include <stdio.h>

void main( void )
{
   char   *string, *stopstring;
   double x;
   long   l;
   int    base;
   unsigned long ul;
   string = "3.1415926This stopped it";
   x = strtod( string, &stopstring );
   printf( "string = %s\n", string );
   printf("   strtod = %f\n", x );
   printf("   Stopped scan at: %s\n\n", stopstring );
   string = "-10110134932This stopped it";
   l = strtol( string, &stopstring, 10 );
   printf( "string = %s", string );
   printf("   strtol = %ld", l );
   printf("   Stopped scan at: %s", stopstring );
   string = "10110134932";
   printf( "string = %s\n", string );
   /* Convert string using base 2, 4, and 8: */
   for( base = 2; base <= 8; base *= 2 )
   {
      /* Convert the string: */
      ul = strtoul( string, &stopstring, base );
      printf( "   strtol = %ld (base %d)\n", ul, base );
      printf( "   Stopped scan at: %s\n", stopstring );
   }
}


Output

string = 3.1415926This stopped it
   strtod = 3.141593
   Stopped scan at: This stopped it

string = -10110134932This stopped it   strtol = -2147483647   Stopped scan at: This stopped itstring = 10110134932
   strtol = 45 (base 2)
   Stopped scan at: 34932
   strtol = 4423 (base 4)
   Stopped scan at: 4932
   strtol = 2134108 (base 8)
   Stopped scan at: 932

0
 
LVL 86

Accepted Solution

by:
jkr earned 800 total points
ID: 12251980
BTW, regarding the 'std::string' issue - all you have to do is calling the 'c_str()' member of that class before passing it to any of these functions, e.g.

std::string str = "1234";

int i;

i = atoi(str.c_str());

char* pc;

i = (int) strtol(str.c_str(), &pc, 10);

if ( NULL != *pc) {

    // conversion error, probably incorrect numerical format
}
0
 
LVL 17

Assisted Solution

by:rstaveley
rstaveley earned 200 total points
ID: 12254080
Arguably, the most C++-ish way to do it is using std::istringstream:
--------8<--------
#include <iostream>
#include <sstream>

int main()
{
      std::istringstream istr("1234");
      int i;
      istr >> i;
      std::cout << "Value is " << i << '\n';
}
--------8<--------
0
 

Expert Comment

by:poojasureshkumar
ID: 14893408
Hi.
I want to convert string "&H0" into long variable.Can any one help me?
I tried with long.parse(string) and Convert.ToInt64(string)..which will not work because the string argument must contain numneric string value.

Can any one help me .

Advance Thanks,
suresh
0
 
LVL 17

Expert Comment

by:rstaveley
ID: 14893586
You are in the wrong place, suresh, I think you want http:/Programming/Programming_Languages/Dot_Net/VisualC_PLUS_PLUS_DOT_NET/ if you are doing Managed C++ / Whidbey / CLI or whatever we're supposed to call it.

Though, &H0 looks like Visual Basic .NET - see http:/Programming/Programming_Languages/Dot_Net/ for all the .NET goodies.
0

Featured Post

Concerto's Cloud Advisory Services

Want to avoid the missteps to gaining all the benefits of the cloud? Learn more about the different assessment options from our Cloud Advisory team.

Question has a verified solution.

If you are experiencing a similar issue, please ask a related question

Introduction This article is a continuation of the C/C++ Visual Studio Express debugger series. Part 1 provided a quick start guide in using the debugger. Part 2 focused on additional topics in breakpoints. As your assignments become a little more …
Many modern programming languages support the concept of a property -- a class member that combines characteristics of both a data member and a method.  These are sometimes called "smart fields" because you can add logic that is applied automaticall…
The goal of the video will be to teach the user the difference and consequence of passing data by value vs passing data by reference in C++. An example of passing data by value as well as an example of passing data by reference will be be given. Bot…
The viewer will learn additional member functions of the vector class. Specifically, the capacity and swap member functions will be introduced.
Suggested Courses

730 members asked questions and received personalized solutions in the past 7 days.

Join the community of 500,000 technology professionals and ask your questions.

Join & Ask a Question