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When you have a choice of two functions to accomplish the same task, prefer the one with better error checking and reporting.

The following table shows a list of C standard library functions that provide limited or no error checking and reporting along with preferable alternatives:

Noncompliant Code Example (atoi())

This noncompliant code example converts the string token stored in the static array buff to a signed integer value using the atoi() function.:

int si;

if (argc > 1) {
  si = atoi(argv[1]);
}

The atoi(), atol(), and atoll() functions convert the initial portion of a string token to int, long int, and long long int representation , respectively. Except for the behavior on error, they are equivalent to

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as follows:

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...

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...

...

...

...

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...

...

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Unfortunately, atoi() and related functions lack a mechanism for reporting errors for invalid values. Specifically, the atoi(), atol(), and atoll() functions

• do Do not need to set errno on an error.
• have Have undefined behavior if the value of the result cannot be represented. (See undefined behavior 119 of Annex J of the C Standard.)
• Return return 0 if the string does not represent an integer , (which is indistinguishable from a correctly formatted, zero-denoting input string), but the C Standard only specifies the behavior of these functions on success.

See also MSC24-C. Do not use deprecated or obsolescent functions.

Compliant Solution (strtol())

The strtol(), strtoll(), strtoul(), and strtoull() functions convert a null-terminated byte string to long int, long long int, unsigned long int, and unsigned long long int representation , respectively.

This compliant solution uses strtol() to convert a string token to an integer and ensures that the value is in the range of int.:

long sl;
int si;
char *end_ptr;

if (argc > 1) {
  errno = 0;

  sl = strtol(argv[1], &end_ptr, 10);

  if ((sl == LONG_MIN || sl == LONG_MAX)
   && errno != 0)
  {
    perror("strtol error");
  }
  else if (end_ptr == argv[1]) {
    if (puts("error encountered during conversion") == EOF) {
      /* Handle Errorerror */
    }
  }
  else if (sl > INT_MAX) {
    printf("%ld too large!\n", sl);
  }
  else if (sl < INT_MIN) {
    printf("%ld too small!\n", sl);
  }
  else if ('\0' != *end_ptr) {
    if (puts("extra characters on input line\n") == EOF) {
      /* Handle Errorerror */
    }
  }
  else {
    si = (int)sl;
  }
}

Both the non-compliant noncompliant code example and compliant the compliant solution are taken from INT06ERR34-C. Use strtol() or a related function to convert a string token to an integerDetect errors when converting a string to a number.

Noncompliant Code Example (rewind())

This noncompliant code example sets the file position indicator of an input stream back to the beginning using rewind().:

char *file_name;
FILE *fp;

/* initializeInitialize file_name */

fp = fopen(file_name, "r");
if (fp == NULL) {
  /* Handle open error */
}

/* readRead data */

rewind(fp);

/* continueContinue */

However, it It is impossible to determine if rewind() succeeded.

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This compliant solution uses fseek() instead of rewind() and checks to see if the operation succeeded.:

char *file_name;
FILE *fp;

/* initializeInitialize file_name */

fp = fopen(file_name, "r");
if (fp == NULL) {
  /* Handle open error */
}

/* readRead data */

if (fseek(fp, 0L, SEEK_SET) != 0) {
  /* Handle repositioning error */
}

/* continueContinue */

Both the non-compliant code example and compliant solution are taken from FIO07-C. Prefer fseek() to rewind().

Noncompliant Code Example (setbuf())

This noncompliant code example calls setbuf() with a buf argument of NULL.:

FILE *file;
/* Setup file */
setbuf(file, NULL);
/* ... */

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This compliant solution calls setvbuf(), which returns nonzero if the operation failed.:

FILE *file;
char *buf = NULL;
/* Setup file */
if (setvbuf(file, buf, buf ? _IOFBF : _IONBF, BUFSIZ) != 0) {
  /* Handle error */
}
/* ... */

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Risk Assessment

While it Although it is rare for a violation of this rule to result in a security vulnerability, it can easily result in lost or misinterpreted data.

Automated Detection

This rule in general cannot be detected, although various examples can be detected by simply scanning for functions that have equivalent functions with better error handling.

Related Vulnerabilities

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

References

\[[Klein 02|AA. C References#Klein 02]\]
\[[ISO/IEC 9899:1999|AA. C References#ISO/IEC 9899-1999]\] Section 7.20.1.4, "The {{strtol}}, {{strtoll}}, {{strtoul}}, and {{strtoull}} functions," Section 7.20.1.2, "The {{atoi}}, {{atol}}, and {{atoll}} functions," Section 7.19.6.7, "The {{sscanf}} function," Section 7.19.5.5, "The {{setbuf}} function", Section 7.19.9.2, "The fseek function"; 7.19.9.5, and "The rewind function"
\[[MITRE 07|AA. C References#MITRE 07]\] [CWE ID 676|http://cwe.mitre.org/data/definitions/676.html], "Use of Potentially Dangerous Function," and [CWE ID 20|http://cwe.mitre.org/data/definitions/20.html], "Insufficient Input Validation"

Related Guidelines

Bibliography

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Image Added Image Added Image AddedImage Removed      12. Error Handling (ERR)      ERR31-C. Don't redefine errno