详解GNU C库函数大全：必备资源

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"C库函数介绍大全英文版"是一份详尽的文档，专为GNU C Library（GNU C标准库）提供参考。该版本是0.10版，发布于2001年7月6日，适用于当时的GNU C Library 2.3.x系列。这份文档由Free Software Foundation (FSF) 授权使用，遵循GNU Free Documentation License，版本1.1或更高版本。该许可允许用户在特定条件下复制、分发和修改文档，其中包括了“FreeSoftwareNeedsFreeDocumentation”和“GNULesserGeneralPublicLicense”两个不变节部分。文档的主要内容涵盖了C语言标准库的广泛功能，包括输入输出（I/O）、字符串处理、数学运算、内存管理、文件操作、系统调用以及众多实用函数。C库函数是C编程的基础，它们为程序员提供了丰富的工具，使得编写高效且功能强大的程序成为可能。例如，stdio.h中的<stdio>库提供基本的输入输出功能，如printf()和scanf()；stdlib.h中的<cstdlib>库包含内存分配和管理函数如malloc()和free()；而string.h中的<string.h>库则支持字符串操作，如strcpy()和strlen()。在介绍每个函数时，文档通常会详细解释函数的功能、参数、返回值以及可能遇到的错误和注意事项。此外，还会有示例代码来帮助读者理解和应用这些库函数。对于高级开发者来说，这份文档是一个宝贵的资源，它不仅有助于深入理解C语言的内在机制，还能提升代码质量和性能。在阅读这份文档时，用户不仅可以学习如何使用这些现成的函数，还可以借此了解C语言的设计思想和库函数组织结构，这对于提升编程技能和优化程序设计至关重要。同时，由于版本更新频繁，确保查阅的是最新版可以帮助避免与新特性不兼容的问题。总结而言，"C库函数介绍大全英文版"是C语言开发者必备的学习资料，无论你是初学者还是经验丰富的程序员，都能从中找到所需的信息，提升编程效率和代码质量。通过深入研究和实践，你将能够熟练掌握C库并为你的项目开发打下坚实的基础。

features, it is harmless to define in addition a feature test macro for

a subset of those features. For example, if you define

`_POSIX_C_SOURCE', then defining `_POSIX_SOURCE' as well has no effect.

Likewise, if you define `_GNU_SOURCE', then defining either

`_POSIX_SOURCE' or `_POSIX_C_SOURCE' or `_SVID_SOURCE' as well has no

effect.

Note, however, that the features of `_BSD_SOURCE' are not a subset of

any of the other feature test macros supported. This is because it

defines BSD features that take precedence over the POSIX features that

are requested by the other macros. For this reason, defining

`_BSD_SOURCE' in addition to the other feature test macros does have an

effect: it causes the BSD features to take priority over the conflicting

POSIX features.

Roadmap to the Manual

=====================

Here is an overview of the contents of the remaining chapters of this

manual.

* *Note Error Reporting::, describes how errors detected by the

library are reported.

* *Note Language Features::, contains information about library

support for standard parts of the C language, including things

like the `sizeof' operator and the symbolic constant `NULL', how

to write functions accepting variable numbers of arguments, and

constants describing the ranges and other properties of the

numerical types. There is also a simple debugging mechanism which

allows you to put assertions in your code, and have diagnostic

messages printed if the tests fail.

* *Note Memory::, describes the GNU library's facilities for

managing and using virtual and real memory, including dynamic

allocation of virtual memory. If you do not know in advance how

much memory your program needs, you can allocate it dynamically

instead, and manipulate it via pointers.

* *Note Character Handling::, contains information about character

classification functions (such as `isspace') and functions for

performing case conversion.

* *Note String and Array Utilities::, has descriptions of functions

for manipulating strings (null-terminated character arrays) and

general byte arrays, including operations such as copying and

comparison.

* *Note I/O Overview::, gives an overall look at the input and output

facilities in the library, and contains information about basic

concepts such as file names.

* *Note I/O on Streams::, describes I/O operations involving streams

(or `FILE *' objects). These are the normal C library functions

from `stdio.h'.

* *Note Low-Level I/O::, contains information about I/O operations

on file descriptors. File descriptors are a lower-level mechanism

specific to the Unix family of operating systems.

* *Note File System Interface::, has descriptions of operations on

entire files, such as functions for deleting and renaming them and

for creating new directories. This chapter also contains

information about how you can access the attributes of a file,

such as its owner and file protection modes.

* *Note Pipes and FIFOs::, contains information about simple

interprocess communication mechanisms. Pipes allow communication

between two related processes (such as between a parent and

child), while FIFOs allow communication between processes sharing

a common file system on the same machine.

* *Note Sockets::, describes a more complicated interprocess

communication mechanism that allows processes running on different

machines to communicate over a network. This chapter also

contains information about Internet host addressing and how to use

the system network databases.

* *Note Low-Level Terminal Interface::, describes how you can change

the attributes of a terminal device. If you want to disable echo

of characters typed by the user, for example, read this chapter.

* *Note Mathematics::, contains information about the math library

functions. These include things like random-number generators and

remainder functions on integers as well as the usual trigonometric

and exponential functions on floating-point numbers.

* *Note Low-Level Arithmetic Functions: Arithmetic, describes

functions for simple arithmetic, analysis of floating-point

values, and reading numbers from strings.

* *Note Searching and Sorting::, contains information about functions

for searching and sorting arrays. You can use these functions on

any kind of array by providing an appropriate comparison function.

* *Note Pattern Matching::, presents functions for matching regular

expressions and shell file name patterns, and for expanding words

as the shell does.

* *Note Date and Time::, describes functions for measuring both

calendar time and CPU time, as well as functions for setting

alarms and timers.

* *Note Character Set Handling::, contains information about

manipulating characters and strings using character sets larger

than will fit in the usual `char' data type.

* *Note Locales::, describes how selecting a particular country or

language affects the behavior of the library. For example, the

locale affects collation sequences for strings and how monetary

values are formatted.

* *Note Non-Local Exits::, contains descriptions of the `setjmp' and

`longjmp' functions. These functions provide a facility for

`goto'-like jumps which can jump from one function to another.

* *Note Signal Handling::, tells you all about signals--what they

are, how to establish a handler that is called when a particular

kind of signal is delivered, and how to prevent signals from

arriving during critical sections of your program.

* *Note Program Basics::, tells how your programs can access their

command-line arguments and environment variables.

* *Note Processes::, contains information about how to start new

processes and run programs.

* *Note Job Control::, describes functions for manipulating process

groups and the controlling terminal. This material is probably

only of interest if you are writing a shell or other program which

handles job control specially.

* *Note Name Service Switch::, describes the services which are

available for looking up names in the system databases, how to

determine which service is used for which database, and how these

services are implemented so that contributors can design their own

services.

* *Note User Database::, and *Note Group Database::, tell you how to

access the system user and group databases.

* *Note System Management::, describes functions for controlling and

getting information about the hardware and software configuration

your program is executing under.

* *Note System Configuration::, tells you how you can get

information about various operating system limits. Most of these

parameters are provided for compatibility with POSIX.

* *Note Library Summary::, gives a summary of all the functions,

variables, and macros in the library, with complete data types and

function prototypes, and says what standard or system each is

derived from.

* *Note Maintenance::, explains how to build and install the GNU C

library on your system, how to report any bugs you might find, and

how to add new functions or port the library to a new system.

If you already know the name of the facility you are interested in,

you can look it up in *Note Library Summary::. This gives you a

summary of its syntax and a pointer to where you can find a more

detailed description. This appendix is particularly useful if you just

want to verify the order and type of arguments to a function, for

example. It also tells you what standard or system each function,

variable, or macro is derived from.

Error Reporting

***************

Many functions in the GNU C library detect and report error conditions,

and sometimes your programs need to check for these error conditions.

For example, when you open an input file, you should verify that the

file was actually opened correctly, and print an error message or take

other appropriate action if the call to the library function failed.

This chapter describes how the error reporting facility works. Your

program should include the header file `errno.h' to use this facility.

Checking for Errors

===================

Most library functions return a special value to indicate that they have

failed. The special value is typically `-1', a null pointer, or a

constant such as `EOF' that is defined for that purpose. But this

return value tells you only that an error has occurred. To find out

what kind of error it was, you need to look at the error code stored in

the variable `errno'. This variable is declared in the header file

`errno.h'.

- Variable: volatile int errno

The variable `errno' contains the system error number. You can

change the value of `errno'.

Since `errno' is declared `volatile', it might be changed

asynchronously by a signal handler; see *Note Defining Handlers::.

However, a properly written signal handler saves and restores the

value of `errno', so you generally do not need to worry about this

possibility except when writing signal handlers.

The initial value of `errno' at program startup is zero. Many

library functions are guaranteed to set it to certain nonzero

values when they encounter certain kinds of errors. These error

conditions are listed for each function. These functions do not

change `errno' when they succeed; thus, the value of `errno' after

a successful call is not necessarily zero, and you should not use

`errno' to determine _whether_ a call failed. The proper way to

do that is documented for each function. _If_ the call failed,

you can examine `errno'.

Many library functions can set `errno' to a nonzero value as a

result of calling other library functions which might fail. You

should assume that any library function might alter `errno' when

the function returns an error.

*Portability Note:* ISO C specifies `errno' as a "modifiable

lvalue" rather than as a variable, permitting it to be implemented

as a macro. For example, its expansion might involve a function

call, like `*_errno ()'. In fact, that is what it is on the GNU

system itself. The GNU library, on non-GNU systems, does whatever

is right for the particular system.

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