Differences between microlib and the default C library

Non-Confidential

PDF version

ARM DUI0378H

ARM^® Compiler v5.06 for µVision^® ARM C and C++ Libraries and Floating-Point Support User Guide

Version 5

Home > The ARM C Micro-library > Differences between microlib and the default C library

2.2 Differences between microlib and the default C library

There are a number of differences between microlib and the default C library.

The main differences are:

Microlib is not compliant with the ISO C library standard. Some ISO features are not supported and others have less functionality.
Microlib is not compliant with the IEEE 754 standard for binary floating-point arithmetic.
Microlib is highly optimized for small code size.
Locales are not configurable. The default C locale is the only one available.
main() must not be declared to take arguments and must not return. In main, argc and argv parameters are undefined and cannot be used to access command-line arguments.

Microlib provides limited support for C99 functions. Specifically, microlib does not support the following C99 functions:

<fenv.h> functions:

feclearexcept      fegetenv           fegetexceptflag
fegetround         feholdexcept       feraiseexcept
fesetenv           fesetexceptflag    fesetround
fetestexcept       feupdateenv

Wide characters in general:

btowc         fgetwc         fgetws         fputwc
fputws        fwide          fwprintf       fwscanf
getwc         getwchar       iswalnum       iswalpha 
iswblank      iswcntrl       iswctype       iswdigit 
iswgraph      iswlower       iswprint       iswpunct 
iswspace      iswupper       iswxdigit      mblen 
mbrlen        mbsinit        mbsrtowcs      mbstowcs 
mbtowc        putwc          putwchar       swprintf 
swscanf       towctrans      towlower       towupper 
ungetwc       vfwprintf      vfwscanf       vswprintf 
vswscanf      vwprintf       vwscanf        wcscat 
wcschr        wcscmp         wcscoll        wcscspn 
wcsftime      wcslen         wcsncat        wcsncmp 
wcsncpy       wcspbrk        wcsrchr        wcsrtombs 
wcsspn        wcsstr         wcstod         wcstof 
wcstoimax     wcstok         wcstol         wcstold 
wcstoll       wcstombs       wcstoul        wcstoull 
wcstoumax     wcsxfrm        wctob          wctomb 
wctrans       wctype         wmemchr        wmemcmp 
wmemcpy       wmemmove       wmemset        wprintf 
wscanf

Auxiliary <math.h> functions:

ilogb              ilogbf             ilogbl 
lgamma             lgammaf            lgammal 
logb               logbf              logbl 
nextafter          nextafterf         nextafterl 
nexttoward         nexttowardf        nexttowardl

Functions relating to program startup and shutdown and other OS interaction:
```
_Exit              atexit             exit
system             time
```

Microlib does not support C++.
Microlib does not support operating system functions.
Microlib does not support position-independent code.
Microlib does not provide mutex locks to guard against code that is not thread safe.
Microlib does not support wide characters or multibyte strings.
Microlib does not support selectable one or two region memory models as the standard library (stdlib) does. Microlib provides only the two region memory model with separate stack and heap regions.
Microlib does not support the bit-aligned memory functions _membitcpy[b|h|w][b|l]() and membitmove[b|h|w][b|l]().
Microlib can be used with either --fpmode=std or --fpmode=fast.
The level of ANSI C stdio support that is provided can be controlled with #pragma import(__use_full_stdio).
#pragma import(__use_smaller_memcpy) selects a smaller, but slower, version of memcpy().
setvbuf() and setbuf() always fail because all streams are unbuffered.
feof() and ferror() always return 0 because the error and EOF indicators are not supported.

Non-Confidential	PDF version	ARM DUI0378H
Copyright © 2007, 2008, 2011, 2012, 2014-2016 ARM. All rights reserved.

Home > The ARM C Micro-library > Differences between microlib and the default C library

Differences between microlib and the default C library

2.2 Differences between microlib and the default C library

Related concepts

Related tasks

Related reference

Related information

Products

Development Tools

Hardware & Collateral

Downloads

Support

Contact

Important information

Privacy Policy Update