【正文】 e C programming language was approved. This standard has also been adopted as international standard ISO/IEC 9899:1990. ANSI is the American National Standards Institute, the . member in the International Organization for Standardization (ISO). IEC stands for the International Electrotechnical Commission.The C standard is now maintained and developed by the ISO/IEC international standardization working group for the C programming language, known as ISO/IEC JTC1/SC22/WG14, or WG14 for short. The intent of the ISO C standard is to provide portability of conforming C programs to a wide variety of operating systems, not only the UNIX System. This standard defines not only the syntax and semantics of the programming language but also a standard library [Chapter 7 of ISO 1999。 Plauger 1992。 Appendix B of Kernighan and Ritchie 1988]. This library is important because all contemporary UNIX systems, such as the ones described in this book, provide the library routines that are specified in the C standard.IEEE POSIXPOSIX is a family of standards developed by the IEEE (Institute of Electrical and Electronics Engineers). POSIX stands for Portable Operating System Interface. It originally referred only to the IEEE Standard operating system interfacebut was later extended to include many of the standards and draft standards with the 1003 designation, including the shell and utilities ().Of specific interest to this book is the operating system interface standard, whose goal is to promote the portability of applications among various UNIX System environments. This standard defines the services that must be provided by an operating system if it is to be POSIX pliant, and has been adopted by most puter vendors. Although the standard is based on the UNIX operating system, the standard is not restricted to UNIX and UNIXlike systems. Indeed, some vendors supplying proprietary operating systems claim that these systems have been made POSIX pliant, while still leaving all their proprietary features in place.Because the standard specifies an interface and not an implementation, no distinction is made between system calls and library functions. All the routines in the standard are called functions.Standards are continually evolving, and the standard is no exception. The 1988 version of this standard, IEEE Standard , was modified and submitted to the International Organization for Standardization. No new interfaces or features were added, but the text was revised. The resulting document was published as IEEE Std [IEEE 1990]. This is also the international standard ISO/IEC 99451:1990. This standard is monly referred to as , which we39。ll use in this text.The IEEE working group continued to make changes to the standard. In 1993, a revised version of the IEEE standard was published. It included standard and the realtime extensions standard. In 1996, the standard was again updated as international standard ISO/IEC 99451:1996. It included interfaces for multithreaded programming, called pthreads for POSIX threads. More realtime interfaces were added in 1999 with the publication of IEEE Standard . A year later, IEEE Standard was published, including even more realtime interfaces, and IEEE Standard was published, adding eventtracing extensions to the standard. does not include the notion of a superuser. Instead, certain operations require appropriate privileges, although leaves the definition of this term up to the implementation. UNIX systems that conform to the Department of Defense security guidelines have many levels of security. In this text, however, we use the traditional terminology and refer to operations that require superuser privilege.附錄BU N I X和C程序設(shè)計(jì)語言的標(biāo)準(zhǔn)化工作已經(jīng)做了很多。雖然U N I X應(yīng)用程序在不同的U N I X版本之間進(jìn)行移植相當(dāng)容易，但是8 0年代U N I X版本的劇增以及它們之間差別的擴(kuò)大導(dǎo)致很多大用戶(例如美國(guó)政府)要求對(duì)其進(jìn)行標(biāo)準(zhǔn)化。本章將介紹正在進(jìn)行的各種標(biāo)準(zhǔn)化工作，然后討論這些標(biāo)準(zhǔn)對(duì)本書所列舉的實(shí)際U N I X實(shí)現(xiàn)的影響。所有標(biāo)準(zhǔn)化工作的一個(gè)重要部分是對(duì)每種實(shí)現(xiàn)必須定義的各種限制的說明，所以我們將說明這些限制以及確定它們值的多種方法。UNIX標(biāo)準(zhǔn)化ISO C1 9 8 9年后期，C程序設(shè)計(jì)語言的A N S I標(biāo)準(zhǔn)X 3 . 1 5 9 1 9 8 9得到批準(zhǔn)〔ANSI 1989〕。此標(biāo)準(zhǔn)已被采用為國(guó)際標(biāo)準(zhǔn)ISO/IEC 9899:1990。A N S I是美國(guó)國(guó)家標(biāo)準(zhǔn)學(xué)會(huì)，它是由制造商和用戶組成的非贏利性組織。在美國(guó)，它是全國(guó)性的無償標(biāo)準(zhǔn)交換站，在國(guó)際標(biāo)準(zhǔn)化組織( I S O )中是代表美國(guó)的成員。ANSI C標(biāo)準(zhǔn)的意圖是提供C程序的可移植性，使其能適合于大量不同的操作系統(tǒng)，而不只是UN I X。此標(biāo)準(zhǔn)不僅定義了C程序設(shè)計(jì)語言的語法和語義，也定義了其標(biāo)準(zhǔn)庫〔ANSI 1989第4章；Plauger 1992。Kernighan及Ritchie 1988中的附錄B〕。因?yàn)楹芏嘈碌腢 N I X系統(tǒng)（例如本書介紹的幾個(gè)U N I X系統(tǒng)）都提供C標(biāo)準(zhǔn)中說明的庫函數(shù)，所以此庫對(duì)我們來講是很重要的。按照該標(biāo)準(zhǔn)定義的各個(gè)頭文件，可將該庫分成1 5區(qū)。表2 1中列出了C標(biāo)準(zhǔn)定義的頭文件，以及下面幾節(jié)中說明的另外兩個(gè)標(biāo)準(zhǔn)( P O S I X . 1和X P G 3 )定義的頭文件。在其中也列舉了S V R 4和4 . 3 + B S D所支持的頭文件。本章也將對(duì)這兩種U N I X實(shí)現(xiàn)進(jìn)行說明。IEEE POSIXP O S I X是一個(gè)由I E E E (電氣和電子工程師學(xué)會(huì))制訂的標(biāo)準(zhǔn)族。P O S I X的意思是計(jì)算機(jī)環(huán)境的可移植操作系統(tǒng)界面(Portable Operating System Interface for Computer Environment)。它原來指的只是I E E E標(biāo)準(zhǔn)1 0 0 3 . 1 1 9 8 8 (操作系統(tǒng)界面)，但是， I E E E目前正在制訂P O S I X族中的其他有關(guān)標(biāo)準(zhǔn)。例如， 1 0 0 3 . 2將是針對(duì)s h e l l和公用程序的標(biāo)準(zhǔn)， 1 0 0 3 . 7將是系統(tǒng)管理方面的標(biāo)準(zhǔn)。在1 0 0 3工作組中至少有1 5個(gè)子委員會(huì)。與本書相關(guān)的是1 0 0 3 . 1操作系統(tǒng)界面標(biāo)準(zhǔn)，該標(biāo)準(zhǔn)定義了“ P O S I X依從的”操作系統(tǒng)必須提供的服務(wù)。雖然1 0 0 3 . 1標(biāo)準(zhǔn)是以U N I X操作系統(tǒng)為基礎(chǔ)的，但是它又不僅僅限于U N I X和類似于U N I X的系統(tǒng)。確實(shí)，有些供應(yīng)專有操作系統(tǒng)的制造商也聲稱這些系統(tǒng)將依從P O S I X (同時(shí)還保有它們的所有專有功能)。由于1 0 0 3 . 1標(biāo)準(zhǔn)說明了一個(gè)界面（ i n t e r f a c e）而不是一種實(shí)現(xiàn)（ i m p l e m e n t a t i o n），所以并不區(qū)分系統(tǒng)調(diào)用和庫函數(shù)。所有在標(biāo)準(zhǔn)中的例程都被稱為函數(shù)。標(biāo)準(zhǔn)是不斷演變的， 1 0 0 3 . 1標(biāo)準(zhǔn)也不例外。該標(biāo)準(zhǔn)的1 9 8 8版，IEEE S O，沒有增加新的界面或功能，但修改了文本。最終的文檔作為IEEE 〔IEEE 1990 〕，這也就是國(guó)際標(biāo)準(zhǔn)ISO/IEC 99451:1990 。該標(biāo)準(zhǔn)通常被稱之為P O S I X . 1，本書將使用此標(biāo)準(zhǔn)。IEEE ，它們?cè)? 9 9 3年被批準(zhǔn)。這些修改(現(xiàn)在稱之為1 0 0 3 . 1 a )應(yīng)由I E E E作為I E E E標(biāo)準(zhǔn)1 0 0 3 . 1 1 9 9 0的附件出版，這些修改也對(duì)本書有所影響，主要是因?yàn)椴死L(fēng)格的符號(hào)鏈接很可能將被加到標(biāo)準(zhǔn)中作為一種要求的功能。這些修改也很可能成為ISO/IEC 99451:1990的一個(gè)附錄。本書將用注釋的方法來說明P O S I X . 1的1 0 0 3 . 1 a版本，指出哪些功能很可能會(huì)加到1 0 0 3 . 1 a中。P O S I X . 1沒有包括超級(jí)用戶這樣的概念。代之以規(guī)定某些操作要求“適當(dāng)?shù)膬?yōu)先權(quán)”，P O S I X . 1將此術(shù)語的定義留由具體實(shí)現(xiàn)進(jìn)行解釋。某些符合國(guó)防部安全性指導(dǎo)原則要求的U n i x系統(tǒng)具有很多不同的安全級(jí)。本書仍使用傳統(tǒng)的U N I X術(shù)語，并指明要求超級(jí)用戶特權(quán)的操作。