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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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It is rare for a violation of this rule to result in a security vulnerability unless it occurs in security-sensitive code. However, violations of this rule can easily result in lost or misinterpreted data. 

Automated Detection

Related Vulnerabilities

Search for vulnerabilities resulting from the violation of this rule on the CERT website.

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Key here (explains table format and definitions)

CERT-CWE Mapping Notes

Key here for mapping notes

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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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