function
<cstdlib>

atoi

int atoi (const char * str);
Convert string to integer
Parses the C-string str interpreting its content as an integral number, which is returned as a value of type int.

The function first discards as many whitespace characters (as in isspace) as necessary until the first non-whitespace character is found. Then, starting from this character, takes an optional initial plus or minus sign followed by as many base-10 digits as possible, and interprets them as a numerical value.

The string can contain additional characters after those that form the integral number, which are ignored and have no effect on the behavior of this function.

If the first sequence of non-whitespace characters in str is not a valid integral number, or if no such sequence exists because either str is empty or it contains only whitespace characters, no conversion is performed and zero is returned.

Parameters

str
C-string beginning with the representation of an integral number.

Return Value

On success, the function returns the converted integral number as an int value.
If the converted value would be out of the range of representable values by an int, it causes undefined behavior. See strtol for a more robust cross-platform alternative when this is a possibility.

Example

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/* atoi example */
#include <stdio.h>      /* printf, fgets */
#include <stdlib.h>     /* atoi */

int main ()
{
  int i;
  char buffer[256];
  printf ("Enter a number: ");
  fgets (buffer, 256, stdin);
  i = atoi (buffer);
  printf ("The value entered is %d. Its double is %d.\n",i,i*2);
  return 0;
}


Output:

Enter a number: 73
The value entered is 73. Its double is 146.

Data races

The array pointed by str is accessed.

Exceptions (C++)

No-throw guarantee: this function never throws exceptions.

If str does not point to a valid C-string, or if the converted value would be out of the range of values representable by an int, it causes undefined behavior.

See also

atol
Convert string to long integer (function )
atof
Convert string to double (function )
strtol
Convert string to long integer (function )

C++