Page History

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The atoi(), atol(), atoll(), and atof() functions convert the initial portion of a string token to int, long int, long long int, and double representation representation, respectively. Except for the behavior on error ([ISO/IEC 9899:2024], s7.24.1.2), they are equivalent to

atoi: (int)strtol(nptr, (char **)NULL, 10)
atol: strtol(nptr, (char **)NULL, 10)
atoll: strtoll(nptr, (char **)NULL, 10)
atof: strtod(nptr, (char **)NULL)

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• do not need to set errno on an error;
• have have undefined behavior 16 if the value of the result cannot be represented;
• return 0 (or 0.0) if the string does not represent an integer (or decimal), which is indistinguishable from a correctly formatted, zero-denoting input string.

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#include <errno.h>
#include <limits.h>
#include <stdlib.h>
#include <stdio.h>
 
void func(const char *buff) {
  char *end;
  int si;

  errno = 0;

  const long sl = strtol(buff, &end, 10);

  if (end == buff) {
    (void) fprintf(stderr, "%s: not a decimal number\n", buff);
  } else if ('\0' != *end) {
    (void) fprintf(stderr, "%s: extra characters at end of input: %s\n", buff, end);
  } else if ((LONG_MIN == sl || LONG_MAX == sl) && ERANGE == errno) {
    (void) fprintf(stderr, "%s out of range of type long\n", buff);
  } else if (sl > INT_MAX) {
    (void) fprintf(stderr, "%ld greater than INT_MAX\n", sl);
  } else if (sl < INT_MIN) {
    (void) fprintf(stderr, "%ld less than INT_MIN\n", sl);
  } else {
    si = (int)sl;

    /* Process si */
  }
}

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Automated Detection

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CWE-391 = Union( ERR34-C, list) where list =

• Failure to errors outside of string-to-number conversion functions

CWE-676 and ERR34-C

• Independent( ENV33-C, CON33-C, STR31-C, EXP33-C, MSC30-C, ERR34-C)

• ERR34-C implies that string-parsing functions (eg atoi() and scanf()) are dangerous.

• CWE-676 = Union( ERR34-C, list) where list =

• Invocation of dangerous functions besides the following:

• atoi(), atol(), atoll(), atof(), The scanf()family

CWE-758 and ERR34-C

Independent( INT34-C, INT36-C, MSC37-C, FLP32-C, EXP33-C, EXP30-C, ERR34-C, ARR32-C)

Intersection( CWE-758, ERR34-C) =

• Undefined behavior arising from a non-representable numeric value being parsed by an ato*() or scanf() function

CWE-758 – ERR34-C =

• Undefined behavior arising from using a function outside of the ato*() or scanf() family

ERR34-C – CWE-758 =

• The ato*() or scanf() family receives input that is not a number when trying to parse one

Bibliography

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