C Implementation-Defined Behavior

A conforming C99 implementation is required to document its choice of behavior for all parts of the language specification that are designated implementation-defined. The tools implementation-defined behavior matches that of GCC 4.2.1 except for the choices listed below.

The following section headings refer to sections in the C99 specification and all choices that depend on an externally determined application binary interface are listed as “determined by ABI,” and are documented in the Application Binary Interface Specification.

Only the supported C99 features are documented.

Environment

• The name and type of the function called at program startup in a freestanding environment (5.1.2.1).

  A hosted environment is provided.

• An alternative manner in which the main function may be defined (5.1.2.2.1).

  There is no alternative manner in which main may be defined.

• The values given to the strings pointed to by argv argument to main (5.1.2.2.1).

  The value of argc is equal to zero. argv[0] is a null pointer. There are no other array members.

• What constitutes an interactive device (5.1.2.3).

  All streams are refer to interactive devices.

• Signal values other than SIGFPE, SIGILL, and SIGSEGV that correspond to a computational exception (7.14.1.1).

  No other signal values correspond to a computational exception.

• Signal values for which is equivalent of signal(sig, SIG_IGN); is executed at program startup (7.14.1.1).

  At program startup the equivalent of signal(sig, SIG_DFL); is executed for all signals.

• The set of environment names and the method for altering the environment list used by the getenv function (7.20.4.5).

  The set of environment names is empty. There is no method for altering the environment list used by the getenv function.

• The manner of execution of the string by the system function used by the getenv function (7.20.4.6).

  This is determined by the execution environment.

Identifiers

• The number of significant initial characters in an identifier (5.2.4.1, 6.4.1).

  All characters in identifiers (with or without external linkage) are significant.

Characters

• The value of the members of the execution character set (5.2.1).

  This is determined by the ASCII character set.

• The unique value of the member of the execution character set produced for each of the standard alphabetic escape sequences (5.2.2).

  This is determined by the ASCII character set.

• The value of a char object into which has been stored any character other than a member of the basic execution set (6.2.5).

  The value of any character other than a member of the basic execution set is determined by the ASCII character set.

• The mapping of members of the source character set (in character constants and string literals) to members of the execution character set (6.4.4.4, 5.1.1.2).

  The source character set is required to be the ASCII character set. Each character in the source character set is mapped to the same character in the execution character set.

• The value of an integer character constant containing more than one character or containing a character or escape sequence that does not map to a single-byte execution character (6.4.4.4).

  The value of an integer character constant containing more than one character is equal to the value of the last character in the character constant. The value of an integer character constant containing a character or escape sequence that does not map to a single-byte execution character is equal to the value reduced modulo 2 ^*n* to be within range of the char type, where n is the number of bits in a char.

• The value of a wide character constant containing more than one multibyte character, or containing a multibyte character or escape multibyte character, or containing a multibyte character or escape sequence not represented in the extended execution character set (6.4.4.4).

  Wide character constants must not contain multibyte characters.

• The current locale used to convert a wide character constant consisting of a single multibyte character that maps to a member of the extended execution character set into a corresponding wide character code (6.4.4.4).

  Wide character constants must not contain multibyte characters.

• The value of a string literal containing a multibyte character or escape sequence not represented in the execution character set (6.4.5).

  String literals must not contain multibyte characters. If an escape sequence not represented in the execution character set is used in a string literal, the value of the corresponding character in the string is the same as the value that would be given to an integer character constant consisting of that escape sequence.

Floating point

• The accuracy of the floating-point operations and of the library functions in <math.h> and <complex.h> that return floating-point results (5.2.4.2.2).

  This is intentionally left undocumented.

• Additional floating-point exceptions, rounding modes, environments, and classifications, and their macros names (7.6, 7.12).

  No additional floating-point exceptions, rounding modes, environments or classifications are defined.

Hints

• The extent to which suggestions made by using the register storage-class specifier are effective (6.7.1).

  The register specifier is ignored except when used as part of the register variable extension.

Preprocessing directives

• The behavior on each recognized non-STDC #pragma directive (6.10.6).

  This is documented in XCC Pragma Directives.

Library functions

• Any library facilities available to a freestanding program, other than the minimal set required by clause 4 (5.1.2.1).

  A hosted environment is provided.

• The format of the diagnostic printed by the assert macro (7.2.1.1).

  The assert macro uses the format “Assertion failed: expression, file filename, line line number, function: function.” where expression is the text of the argument, filename is the value of __FILE__, line number is the value of __LINE__ and function is the name of the current function. If the name of the current function cannot be determined, this part of the message is omitted.

• The representation of the floating-point status flags stored by the fegetexceptflag function (7.6.2.2).

  The function fegetexceptflag is not supported.

• Whether the feraiseexcept function raises the “inexact” floating-point exception in addition to the “overflow” and “underflow” floating-point exception (7.6.2.3).

  The function feraiseexcept is not supported.

• Strings other than "C" and "" that may be passed as the second argument to the setlocale function (7.11.1.1).

  No other strings may be passed as the second argument to the setlocale function.

• The types defined for float_t and double_t when the value of the FLT_EVAL_METHOD macro is less than 0 or greater than 2 (7.12).

  No other values of the FLT_EVAL_METHOD macro are supported.

• Domain errors for the mathematics functions, other than those required by this International Standard (7.12.1).

  This is intentionally left undocumented.

• The values returned by the mathematics functions on domain errors (7.12.1).

  This is intentionally left undocumented.

• The values returned by the mathematics functions on underflow range errors, whether errno is set to the value of the macro ERANGE when the integer expression math_errhandling         & MATH_ERRNO is nonzero, and whether the “underflow” floating-point exception is raised when the integer expression math_errhandling & MATH_ERREXCEPT is nonzero (7.12.1).

  This is intentionally left undocumented.

• Whether a domain error occurs or zero is returned when an fmod function has a second argument of zero (7.12.10.1).

  A domain error occurs when an fmod function has a second argument of zero.

• The base-2 logarithm of the modulus used by the remquo functions in reducing the quotient (7.12.10.3).

  The quotient is reduced modulo 2 ⁷.

• Whether the equivalent of signal(sig, SIG_DFL); is executed prior to the call of a signal handler, and, if not, the blocking of signals that is performed (7.14.1.1).

  The equivalent of signal(sig, SIG_DFL); is executed prior to the call of a signal handler.

• The null pointer constant to which the macro NULL expands (7.17).

  NULL is defined as ((void *)0).

• Whether the last line of a text stream requires a terminating new-line character (7.19.2).

  This is determined by the execution environment.

• Whether space characters that are written out to a text stream immediately before a newline character appear when read in (7.19.2).

  This is determined by the execution environment.

• The number of null characters that may be appended to data written to a binary stream (7.19.2).

  This is determined by the execution environment.

• Whether the file position indicator of an append-mode stream is initially positioned at the beginning or end of a file (7.19.3).

  This is determined by the execution environment.

• Whether a write on a text stream causes the associated file to be truncated beyond that point (7.19.3).

  This is determined by the execution environment.

• The characteristics of file buffering (7.19.3).

  A buffered output stream saves characters until the buffer is full and then writes the characters as a block. A line buffered output stream saves characters until the line is complete or the buffer is full and then writes the characters as a block. An unbuffered output stream writes characters to the destination file immediately.

• Whether a zero-length file actually exists (7.19.3).

  This is determined by the execution environment.

• The rules for composing valid file names (7.19.3).

  This is determined by the execution environment.

• Whether the same file can be simultaneously opened multiple times (7.19.3).

  This is determined by the execution environment.

• The nature and choice of encodings used for multibyte characters in files (7.19.3).

  The execution character set must not contain multibyte characters.

• The effect of the remove function on an open file (7.19.4.1).

  This is determined by the execution environment.

• The effect if a file with the new name exists prior to a call to the rename function (7.19.4.1).

  This is determined by the execution environment.

• Whether an open temporary file is removed upon abnormal program termination (7.19.4.3).

  Temporary files are not removed on abnormal program termination.

• Which changes of mode are permitted (if any), and under what circumstances (7.19.5.4).

  The file cannot be given a more permissive access mode (for example, a mode of “w” will fail on a read-only file descriptor), but can change status such as append or binary mode. If modification is not possible, failure occurs.

• The style used to print an infinity or NaN, and the meaning of any n-char or n-wchar sequence printed for a NaN (7.19.6.1, 7.24.2.1).

  A double argument representing infinity is converted in the style [-]inf. A double argument representing a NaN is converted in the style as nan.

• The output for %p conversion in the fprintf or fwprintf function (7.19.6.1, 7.24.2.1).

  The value of the pointer is converted to unsigned hexadecimal notation in the style dddd; the letters abcdef are used for the conversion. The precision specifies the minimum number of digits to appear; if the value being converted can be represented in fewer digits, it is expanded with leading zeros. The default precision is 1. The characters 0x are prepended to the output.

  The fwprintf function is unsupported.

• The interpretation of a - character that is neither the first nor the last character, nor the second where a ^ character is the first, in the scanlist for %[ conversion in the fscanf or fwscanf function (7.19.6.2, 7.24.2.1).

  The - character is considered to define a range if the character following it is numerically greater than the character before it. Otherwise the - character itself is added to the scanset.

  The fwscanf function is unsupported.

• The set of sequences matched by a %p conversion and the interpretation of the corresponding input item in the fscanf or fwscanf function (7.19.6.2, 7.24.2.2).

  %p matches the same format as %x. The corresponding input item is converted to a pointer.

  The fwscanf function is unsupported.

• The meaning of any n-char or n-wchar sequence in a string representing NaN that is converted by the strtod, strtof, strtold, wcstod, wcstof or wcstold function (7.20.1.3, 7.24.4.1.1).

  The functions wcstod, wcstof and wcstold are not supported. A n-char sequence in a string representing NaN is scanned in hexadecimal form. Any characters which are not hexadecimal digits are ignored.

• Whether or not the strtod, strtof, strtold, wcstod, wcstof or wcstold function sets errno to ERANGE when underflow occurs (7.20.1.3, 7.24.4.1.1).

  The functions wcstod, wcstof and wcstold are not supported. The functions strtod, strtof and strtold do not set errno to ERANGE when and return 0 when underflow occurs.

• Whether the calloc, malloc, and realloc functions return a null pointer or a pointer to an allocated object when the size requested is zero (7.20.3).

  The functions calloc, malloc and realloc functions all return a pointer to an allocated object when the size requested is zero.

• Whether open streams with unwritten buffered data are flushed, open streams are closed, or temporary files are removed when the abort or _Exit function is called (7.20.4.1, 7.20.4.3, 7.20.4.4).

  When the abort function or _Exit function is called, temporary files are not removed, buffered files are not flushed and open streams are left open.

• The termination status returned to the host environment by the abort, exit or _Exit function (7.20.3).

  The function abort causes a software exception to be raised. The termination status returned to the host environment by the functions exit and _Exit is determined by the execution environment.

• The value returned by the system function when its argument is not a null pointer (7.20.4.6).

  This is determined by the execution environment.

• The range and precision of times representable in clock_t and time_t (7.23.1).

  The precision of times representable in time_t is defined by the execution environment. time_t designates an unsigned long. The actual range of times representable by time_t is defined by the execution environment.

  The macro CLOCKS_PER_SEC is defined as 1000. clock_t designates an unsigned long.

• The era for the clock function (7.23.2.1).

  The clock function always returns the value (clock_t)(-1) to indicate that the processor time used is not available.

• The replacement string for the %Z specifier to the strftime and wcsftime functions in the "C" locale (7.23.3.5, 7.24.5.1).

  The %Z specifier is replaced with the string “GMT”.

Locale-Specific Behavior

• Additional members of the source and execution character sets beyond the basic character set (5.2.1).

  Both the source and execution character sets include all members of the ASCII character set.

• The presence, meaning, and representation of additional multibyte characters in the execution character set beyond the basic character set (5.2.1.2).

  The execution character set does not contain multibyte characters.

• The shift states used for the encoding of multibyte characters (5.2.1.2).

  The source and execution character sets does not contain multibyte characters.

• The direction of writing of successive printing characters (5.2.2).

  Characters are printed from left to right.

• The decimal-point character (7.1.1).

  The decimal-point character is ‘.’.

• The set of printing characters (7.4, 7.25.2).

  This is determined by the ASCII character set.

• The set of control characters (7.4, 7.25.2).

  This is determined by the ASCII character set.

• The set of characters tested for by the isalpha, isblank, islower, ispunct, isspace, isupper, iswalpha, iswblank, iswlower, iswpunct, iswspace, or iswupper functions (7.4.1.2, 7.4.1.3, 7.4.1.7, 7.4.1.9, 7.4.1.10, 7.4.1.11, 7.25.2.1.2, 7.25.2.1.3, 7.25.2.1.7, 7.25.2.1.9, 7.25.2.1.10, 7.25.2.1.11).

  The functions isblank, iswalpha, iswblank, iswlower, iswpunct, iswspace and iswupper are not supported.

  islower tests for the characters ‘a to ‘z’. isupper tests for the characters ‘A’ to ‘Z’. isspace tests for the characters ‘ ‘, ‘\f’, ‘\n’, ‘\r’, ‘\t’ and ‘\v’. isalpha tests for upper and lower case characters. ispunct tests for all printable characters except space and alphanumeric characters.

• The native environment (7.11.1.1).

  The native environment is the same as the minimal environment for C translation.

• Additional subject sequences accepted by the numerical conversion functions (7.20.1, 7.24.4.1).

  No additional subject sequences are accepted by the numerical conversion functions.

• The collation sequence of the execution character set (7.21.4.3, 7.24.4.4.2).

  The comparison carried out by the function strcoll is identical to the comparison carried out by the function strcmp.

• The contents of the error message strings set up by the strerror function (7.21.4.3, 7.24.4.4.2).

  The contents of the error message strings are given in Error message strings.

  Error message strings

  Value	String
  EPERM	Not owner
  ENOENT	No such file or directory
  EINTR	Interrupted system call
  EIO	I/O error
  ENXIO	No such device or address
  EBADF	Bad file number
  EAGAIN	No more processes
  ENOMEM	Not enough space
  EACCES	Permission denied
  EFAULT	Bad address
  EBUSY	Device or resource busy
  EEXIST	File exists
  EXDEV	Cross-device link
  ENODEV	No such device
  ENOTDIR	Not a directory
  EISDIR	Is a directory
  EINVAL	Invalid argument
  ENFILE	Too many open files in system
  EMFILE	Too many open files
  ETXTBSY	Text file busy
  EFBIG	File too large
  ENOSPC	No space left on device
  ESPIPE	Illegal seek
  EROFS	Read-only file system
  EMLINK	Too many links
  EPIPE	Broken pipe
  EDOM	Math argument
  ERANGE	Result too large
  ENAMETOOLONG	File or path name too long
  ENOSYS	Function not implemented
  ENOTEMPTY	Directory not empty
  ELOOP	Too many symbolic links

• Character classifications that are supported by the iswctype function (7.25.1).

  The character classifications supported by iswctype are given in Wide character mappings.

  Wide character mappings

  Value	Description
  WCT_TOLOWER	Convert to lower case
  WCT_TOUPPER	Convert to upper case