Reference
C Library
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C Library
cassert (assert.h)
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cmath (math.h)
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cstddef (stddef.h)
cstdio (stdio.h)
cstdlib (stdlib.h)
cstring (string.h)
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cstdlib (stdlib.h)
functions:
abort
abs
atexit
atof
atoi
atol
bsearch
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div
exit
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functions (non-standard):
itoa
macros:
EXIT_FAILURE
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NULL
RAND_MAX
types:
div_t
ldiv_t
size_t


atoi

function
<cstdlib>
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 an int value.

The function first discards as many whitespace characters 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 numerical 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.

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 no valid conversion could be performed, a zero value is returned.
If the correct value is out of the range of representable values, INT_MAX or INT_MIN is returned.

Example

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/* atoi example */
#include <stdio.h>
#include <stdlib.h>
int main ()
{
  int i;
  char szInput [256];
  printf ("Enter a number: ");
  fgets ( szInput, 256, stdin );
  i = atoi (szInput);
  printf ("The value entered is %d. The double is %d.\n",i,i*2);
  return 0;
}


Output:

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

See also

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