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Do not use deprecated or obsolete obsolescent functions when more secure equivalent functions are available. Deprecated functions are defined by the C Standard. Obsolete functions are typically functions for which there are more secure or portable alternatives available and are Obsolescent functions are defined by this rulerecommendation.

Deprecated Functions

The gets() function was deprecated by Technical Corrigendum 3 to C99 and eliminated from C11.  The Annex K gets_s() function is a recommended alternative to gets().

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Obsolescent Functions

Functions in the first column of the following table are hereby defined to be obsolete obsolescent functions. To remediate invocations of obsolete obsolescent functions, an application might use inline coding that, in all respects, conforms to this guideline, or an alternative library that, in all respects, conforms to this guideline, or alternative nonobsolete non-obsolescent functions.

The atof(), atoi(), atol(), and atoll() functions are obsolete obsolescent because the strodstrtod(), strtof(), strtol(), strtold(), strtoll(), strotulstrtoul(), and strtoull() functions can emulate their usage and have more robust error - handling capabilities. See INT05-C. Do not use input functions to convert character data if they cannot handle all possible inputs.

The fopen() and freopen() functions are obsolete obsolescent because the fopen_s() and freopen_s() functions in C11 Annex K can emulate their usage and improve security by protecting the file from unauthorized access by setting its file protection and opening the file with exclusive access [ISO/IEC 9899:2011WG14 N1173].

The setbuf() function is obsolete obsolescent because setbuf() does not return a value and can be emulated using setvbuf(). See FIO12ERR07-C. Prefer setvbuf() to setbuf()functions that support error checking over equivalent functions that don't.

The rewind() function is obsolete obsolescent because rewind() does not return a value and can be emulated using fseek(). See FIO07ERR07-C. Prefer fseek() to rewind()functions that support error checking over equivalent functions that don't.

The asctime() and ctime() functions are

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obsolescent because they use non-reentrant static buffers and can be emulated using asctime_s() and ctime_s().

Unchecked

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Obsolescent Functions

The following If you are using platforms that support Annex K, then functions in the first column of the following table are hereby defined to be unchecked obsolete functions:

To remediate invocations of unchecked obsolete functions, an application might use inline coding that, in all respects, conforms to this guideline, or an alternative library that, in all respects, conforms to this guideline, or alternative nonobsolete functions from C11 Annex K  [ISO/IEC 9899:2011]:

obsolescent functions, with functions in the second column being the recommended alternatives from Annex K.

For information on the tmpfile() and tmpfile_s() functions, see FIO21-C. Do not create temporary files in shared directories.
For information on the memset() and memset_s() functions, see MSC06-C. Beware of compiler optimizations.

To remediate invocations of obsolescent functions, an application might use any of the following recommended functions from ISO/IEC TR 24731-2, Extensions to the C Library—Part II: Dynamic Allocation Functions [ISO/IEC TR 24731-2]or alternative nonobsolete functions from ISO/IEC TR 24731-2:2010 (Part II):

Noncompliant Code Example

In this noncompliant code example, the obsolete obsolescent functions strcat() and strcpy() are used:

#include <string.h>
#include <stdio.h>
 
enum { BUFSIZE = 32 };
void complain(const char *msg) {

  static const char prefix[] = "Error: ";
  static const char suffix[] = "\n";
  char buf[BUFSIZE];

  strcpy(buf, prefix);
  strcat(buf, msg);
  strcat(buf, suffix);
  fputs(buf, stderr);
}

Compliant Solution

In this compliant solution, strcat() and strcpy() are replaced by strcat_s() and strcpy_s():

#define __STDC_WANT_LIB_EXT1__
#include <string.h>
#include <stdio.h>
 
enum { BUFFERSIZE = 256 };

void complain(const char *msg) {
  static const char prefix[] = "Error: ";
  static const char suffix[] = "\n";
  char buf[BUFFERSIZE];

  strcpy_s(buf, BUFFERSIZE, prefix);
  strcat_s(buf, BUFFERSIZE, msg);
  strcat_s(buf, BUFFERSIZE, suffix);
  fputs(buf, stderr);
}

Exceptions

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Risk Assessment

The deprecated and obsolete obsolescent functions enumerated in this guideline are commonly associated with software vulnerabilities.

Automated Detection

Related Vulnerabilities

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

Related Guidelines

Bibliography

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