RealView® Compilation Tools Compiler and Libraries Guide 5.14.1. ISO C library implementation definition

5.14.1. ISO C library implementation definition

The ISO specification leaves some details to the implementors, but requires that implementation choices be documented. This section describes the ARM library implementation.

In the generic ARM C library:

The macro NULL expands to the integer constant 0.
If a program redefines a reserved external identifier, an error might occur when the program is linked with the standard libraries. If it is not linked with standard libraries, no error is diagnosed.
The __aeabi_assert() function prints details of the failing diagnostic on stderr and then calls the abort() function:

*** assertion failed: expression, file name, line number

Note
The behavior of the assert macro depends on the conditions in operation at the most recent occurrence of #include <assert.h> (see Exiting from an assert for details).

The following functions test for character values in the range EOF (–1) to 255 (inclusive):

isalnum()
isalpha()
iscntrl()
islower()
isprint()
isupper()
ispunct().

The ISO C library variants are listed in Library naming conventions.

Mathematical functions

Table 5.18 shows how the mathematical functions respond when supplied with out-of-range arguments.

Table 5.18. Mathematical functions

Function	Condition	Returned value	Error number
`acos(x)`	`abs(x) > 1`	`QNaN`	`EDOM`
`asin(x)`	`abs(x) > 1`	`QNaN`	`EDOM`
`atan2(x,y)`	`x =0, y = 0`	`QNaN`	`EDOM`
`atan2(x,y)`	`x = Inf, y = Inf`	`QNaN`	`EDOM`
`cos(x)`	`x=Inf`	`QNaN`	`EDOM`
`cosh(x)`	Overflow	`+Inf`	`ERANGE`
`exp(x)`	Overflow	`+Inf`	`ERANGE`
`exp(x)`	Underflow	`+0`	`ERANGE`
`fmod(x,y)`	`x=Inf`	`QNaN`	`EDOM`
`fmod(x,y)`	`y = 0`	`QNaN`	`EDOM`
`log(x)`	`x < 0`	`QNaN`	`EDOM`
`log(x)`	`x = 0`	`-Inf`	`EDOM`
`log10(x)`	`x < 0`	`QNaN`	`EDOM`
`log10(x)`	`x = 0`	`-Inf`	`EDOM`
`pow(x,y)`	Overflow	`+Inf`	`ERANGE`
`pow(x,y)`	Underflow	`0`	`ERANGE`
`pow(x,y)`	`x=0 or x=Inf, y=0`	`+1`	`EDOM`
`pow(x,y)`	`x=+0, y<0`	`-Inf`	`EDOM`
`pow(x,y)`	`x=-0, y<0 and y integer`	`-Inf`	`EDOM`
`pow(x,y)`	`x= -0, y<0 and y non-integer`	`QNaN`	`EDOM`
`pow(x,y)`	`x<0, y non-integer`	`QNaN`	`EDOM`
`pow(x,y)`	`x=1, y=Inf`	`QNaN`	`EDOM`
`sqrt(x)`	`x < 0`	`QNaN`	`EDOM`
`sin(x)`	`x=Inf`	`QNaN`	`EDOM`
`sinh(x)`	Overflow	`+Inf`	`ERANGE`
`tan(x)`	`x=Inf`	`QNaN`	`EDOM`
`atan(x)`	`SNaN`	`SNaN`	None
`ceil(x)`	`SNaN`	`SNaN`	None
`floor(x)`	`SNaN`	`SNaN`	None
`frexp(x)`	`SNaN`	`SNaN`	None
`ldexp(x)`	`SNaN`	`SNaN`	None
`modf(x)`	`SNaN`	`SNaN`	None
`tanh(x)`	`SNaN`	`SNaN`	None

HUGE_VAL is an alias for Inf. Consult the errno variable for the error number. Other than the cases shown in Table 5.18, all functions return QNaN when passed QNaN and throw an invalid operation exception when passed SNaN.

Signal functions

Table 5.19 shows the signals supported by the signal() function.

Table 5.19. Signal functions

Signal	Number	Description	Additional argument
SIGABRT	1	This signal is only used if `abort()` or `assert()` are called by your application.	None
SIGFPE	2	Used to signal any arithmetic exception, for example, division by zero. Used by hard and soft floating-point and by integer division.	A set of bits from {FE_EX_INEXACT, FE_EX_UNDERFLOW, FE_EX_OVERFLOW, FE_EX_DIVBYZERO, FE_EX_INVALID, DIVBYZERO}
SIGILL	3	Illegal instruction.	None
SIGINT	4	Attention request from user.	None
SIGSEGV	5	Bad memory access.	None
SIGTERM	6	Termination request.	None
SIGSTAK	7	Stack overflow was detected.	None
SIGRTRED	8	Redirection failed on a runtime library input/output stream.	Name of file or device being re-opened to redirect a standard stream
SIGRTMEM	9	Out of heap space during initialization or after corruption.	Size of failed request
SIGUSR1	10	User-defined.	User-defined
SIGUSR2	11	User-defined.	User-defined
SIGPVFN	12	A pure virtual function was called from C++.	-
SIGCPPL	13	Exception from C++.	-
SIGOUTOFHEAP	14	Returned by the C++ function `::operator new` when out of heap space.	Size of failed request
reserved	15-31	Reserved.	Reserved
other	> 31	User-defined.	User-defined

A signal number greater than SIGUSR2 can be passed through __raise(), and caught by the default signal handler, but it cannot be caught by a handler registered using signal().

signal() returns an error code if you try to register a handler for a signal number greater than SIGUSR2.

The default handling of all recognized signals is to print a diagnostic message and call exit(). This default behavior applies at program startup and until you change it.

Caution

The IEEE 754 standard for floating-point processing states that the default action to an exception is to proceed without a trap. A raised exception in floating-point calculations does not, by default, generate SIGFPE. You can modify floating-point error handling by tailoring the functions and definitions in fenv.h. See Tailoring error signaling, error handling, and program exit and Chapter 6 Floating-point Support for more details on floating-point.

For all the signals in Table 5.19, when a signal occurs, if the handler points to a function, the equivalent of signal(sig, SIG_DFL) is executed before the call to the handler.

If the SIGILL signal is received by a handler specified to by the signal() function, the default handling is reset.

Input/output characteristics

The generic ARM C library has the following input/output characteristics:

The last line of a text stream does not require a terminating newline character.
Space characters written out to a text stream immediately before a newline character do appear when read back in.
No null characters are appended to a binary output stream.
The file position indicator of an append mode stream is initially placed at the end of the file.
A write to a text stream causes the associated file to be truncated beyond the point where the write occurred if this is the behavior of the device category of the file.
The characteristics of file buffering agree with section 4.9.3 of the ISO C standard. If semihosting is used, the maximum number of open files is limited by the available target memory.
A zero-length file exists, that is, where no characters have been written by an output stream.
A file can be opened many times for reading, but only once for writing or updating. A file cannot simultaneously be open for reading on one stream, and open for writing or updating on another.
Local time zones and Daylight Saving Time are not implemented. The values returned indicate that the information is not available. For example, the gmtime() function always returns NULL.
The status returned by exit() is the same value that was passed to it. For definitions of EXIT_SUCCESS and EXIT_FAILURE, see the header file stdlib.h. The semihosting SVC, however, does not pass the status back to the execution environment.
The error messages returned by the strerror() function are identical to those given by the perror() function.
If the size of area requested is zero, calloc() and realloc() return NULL.
If the size of area requested is zero, malloc() returns a pointer to a zero-size block.
abort() closes all open files and deletes all temporary files.
fprintf() prints %p arguments in lowercase hexadecimal format as if a precision of 8 had been specified. If the variant form (%#p) is used, the number is preceded by the character @.
fscanf() treats %p arguments exactly the same as %x arguments.
fscanf() always treats the character "-" in a %...[...] argument as a literal character.
ftell() and fgetpos() set errno to the value of EDOM on failure.
perror() generates the messages shown in Table 5.20.

Table 5.20. perror() messages

Error	Message
`0`	`No error (errno = 0)`
`EDOM`	`EDOM - function argument out of range`
`ERANGE`	`ERANGE - function result not representable`
`ESIGNUM`	`ESIGNUM - illegal signal number`
Others	`Unknown error`

The following characteristics must be specified in an ISO-compliant implementation (these are unspecified in the ARM C library):

the validity of a filename
whether remove() can remove an open file
the effect of calling the rename() function when the new name already exists
the effect of calling getenv() (the default is to return NULL, no value available)
the effect of calling system()
the value returned by clock().

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5.14.1. ISO C library implementation definition

Note

Mathematical functions

Signal functions

Caution

Input/output characteristics