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C Preprocessor
The C preprocessor is the macro preprocessor for the C, Objective-C and C++ computer programming languages. The preprocessor provides the ability for the inclusion of header files, macro expansions, conditional compilation, and line control. In many C implementations, it is a separate program invoked by the compiler as the first part of translation. The language of preprocessor directives is only weakly related to the grammar of C, and so is sometimes used to process other kinds of text files. History The preprocessor was introduced to C around 1973 at the urging of Alan Snyder and also in recognition of the usefulness of the file-inclusion mechanisms available in BCPL and PL/I. Its original version offered only file inclusion and simple string replacement using #include and #define for parameterless macros, respectively. It was extended shortly after, firstly by Mike Lesk and then by John Reiser, to incorporate macros with arguments and conditional compilation. The ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Preprocessor
In computer science, a preprocessor (or precompiler) is a program that processes its input data to produce output that is used as input in another program. The output is said to be a preprocessed form of the input data, which is often used by some subsequent programs like compilers. The amount and kind of processing done depends on the nature of the preprocessor; some preprocessors are only capable of performing relatively simple textual substitutions and macro expansions, while others have the power of full-fledged programming languages. A common example from computer programming is the processing performed on source code before the next step of compilation. In some computer languages (e.g., C and PL/I) there is a phase of translation known as ''preprocessing''. It can also include macro processing, file inclusion and language extensions. Lexical preprocessors Lexical preprocessors are the lowest-level of preprocessors as they only require lexical analysis, that is, they oper ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
C Trigraph
In computer programming, digraphs and trigraphs are sequences of two and three characters, respectively, that appear in source code and, according to a programming language's specification, should be treated as if they were single characters. Various reasons exist for using digraphs and trigraphs: keyboards may not have keys to cover the entire character set of the language, input of special characters may be difficult, text editors may reserve some characters for special use and so on. Trigraphs might also be used for some EBCDIC code pages that lack characters such as . History The basic character set of the C programming language is a subset of the ASCII character set that includes nine characters which lie outside the ISO 646 invariant character set. This can pose a problem for writing source code when the encoding (and possibly keyboard) being used does not support any of these nine characters. The ANSI C committee invented trigraphs as a way of entering source code using ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Order Of Operations
In mathematics and computer programming, the order of operations (or operator precedence) is a collection of rules that reflect conventions about which procedures to perform first in order to evaluate a given mathematical expression. For example, in mathematics and most computer languages, multiplication is granted a higher precedence than addition, and it has been this way since the introduction of modern algebraic notation. Thus, the expression is interpreted to have the value , and not . When exponents were introduced in the 16th and 17th centuries, they were given precedence over both addition and multiplication, and could be placed only as a superscript to the right of their base. Thus and . These conventions exist to eliminate notational ambiguity, while allowing notation to be as brief as possible. Where it is desired to override the precedence conventions, or even simply to emphasize them, parentheses ( ) can be used. For example, forces addition to precede multipli ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Radian
The radian, denoted by the symbol rad, is the unit of angle in the International System of Units (SI) and is the standard unit of angular measure used in many areas of mathematics. The unit was formerly an SI supplementary unit (before that category was abolished in 1995). The radian is defined in the SI as being a dimensionless unit, with 1 rad = 1. Its symbol is accordingly often omitted, especially in mathematical writing. Definition One radian is defined as the angle subtended from the center of a circle which intercepts an arc equal in length to the radius of the circle. More generally, the magnitude in radians of a subtended angle is equal to the ratio of the arc length to the radius of the circle; that is, \theta = \frac, where is the subtended angle in radians, is arc length, and is radius. A right angle is exactly \frac radians. The rotation angle (360°) corresponding to one complete revolution is the length of the circumference divided by the radius, which i ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Hard Coding
Hard coding (also hard-coding or hardcoding) is the software development practice of embedding data directly into the source code of a program or other executable object, as opposed to obtaining the data from external sources or generating it at runtime. Hard-coded data typically can only be modified by editing the source code and recompiling the executable, although it can be changed in memory or on disk using a debugger or hex editor. Data that are hard-coded is best for unchanging pieces of information, such as physical constants, version numbers and static text elements. Softcoded data, on the other hand, encode arbitrary information through user input, text files, INI files, HTTP server responses, configuration files, preprocessor macros, external constants, databases, command-line arguments, and are determined at runtime. Overview Hard coding requires the program's source code to be changed any time the input data or desired format changes, when it might be more conveni ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Microsoft Windows
Windows is a group of several proprietary graphical operating system families developed and marketed by Microsoft. Each family caters to a certain sector of the computing industry. For example, Windows NT for consumers, Windows Server for servers, and Windows IoT for embedded systems. Defunct Windows families include Windows 9x, Windows Mobile, and Windows Phone. The first version of Windows was released on November 20, 1985, as a graphical operating system shell for MS-DOS in response to the growing interest in graphical user interfaces (GUIs). Windows is the most popular desktop operating system in the world, with 75% market share , according to StatCounter. However, Windows is not the most used operating system when including both mobile and desktop OSes, due to Android's massive growth. , the most recent version of Windows is Windows 11 for consumer PCs and tablets, Windows 11 Enterprise for corporations, and Windows Server 2022 for servers. Genealogy By marketing ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
If Else
In computer science, conditionals (that is, conditional statements, conditional expressions and conditional constructs,) are programming language commands for handling decisions. Specifically, conditionals perform different computations or actions depending on whether a programmer-defined boolean datatype, boolean ''condition'' evaluates to true or false. In terms of control flow, the decision is always achieved by selectively altering the control flow based on some condition (apart from the case of branch predication). Although dynamic dispatch is not usually classified as a conditional construct, it is another way to select between alternatives at run time (program lifecycle phase), runtime. Terminology In imperative programming languages, the term "conditional statement (programming), statement" is usually used, whereas in functional programming, the terms "conditional expression (programming), expression" or "conditional construct" are preferred, because these terms all ha ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Pragma Once
In the C and C++ programming languages, #pragma once is a non-standard but widely supported preprocessor directive designed to cause the current source file to be included only once in a single compilation. Thus, #pragma once serves the same purpose as include guards, but with several advantages, including: less code, avoidance of name clashes, and sometimes improvement in compilation speed. On the other hand, #pragma once is not necessarily available in all compilers and its implementation is tricky and might not always be reliable. Example ;File "grandparent.h" #pragma once struct foo ; ;File "parent.h" #include "grandparent.h" ;File "child.c" #include "grandparent.h" #include "parent.h" In this example, the inclusion of grandparent.h in both parent.h and child.c would ordinarily cause a compilation error, because a struct with a given name can only be defined a single time in a given compilation. The #pragma once directive serves to avoid this by ignoring subsequent i ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Include Guard
In the C and C++ programming languages, an #include guard, sometimes called a macro guard, header guard or file guard, is a particular construct used to avoid the problem of ''double inclusion'' when dealing with the include directive. The C preprocessor processes directives of the form #include in a source file by locating the associated file on disk and transcluding ("including") its contents into a copy of the source file known as the translation unit, replacing the include directive in the process. The files included in this regard are generally header files, which typically contain declarations of functions and classes or structs. If certain C or C++ language constructs are defined twice, the resulting translation unit is invalid. #include guards prevent this erroneous construct from arising by the double inclusion mechanism. The addition of #include guards to a header file is one way to make that file idempotent. Another construct to combat ''double inclusion ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
X BitMap
In computer graphics, the X Window System used X BitMap (XBM), a plain text binary image format, for storing cursor and icon bitmaps used in the X GUI. The XBM format is superseded by XPM, which first appeared for X11 in 1989. Format XBM files differ markedly from most image files in that they take the form of C source files. This means that they can be compiled directly into an application without any preprocessing steps, but it also makes them far larger than their raw pixel data. The image data is encoded as a comma-separated list of byte values, each written in the C hexadecimal notation, '0x13' for example, so that multiple ASCII characters are used to express a single byte of image information. XBM data consists of a series of static unsigned char arrays containing the monochrome pixel data. When the format was in common use, an XBM typically appeared in headers (.h files) which featured one array per image stored in the header. The following piece of C code exemplifie ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Make (software)
In software development, Make is a build automation tool that automatically builds executable programs and libraries from source code by reading files called ''Makefiles'' which specify how to derive the target program. Though integrated development environments and language-specific compiler features can also be used to manage a build process, Make remains widely used, especially in Unix and Unix-like operating systems. Besides building programs, Make can be used to manage any project where some files must be updated automatically from others whenever the others change. Origin There are now a number of dependency-tracking build utilities, but Make is one of the most widespread, primarily due to its inclusion in Unix, starting with the PWB/UNIX 1.0, which featured a variety of tools targeting software development tasks. It was originally created by Stuart Feldman in April 1976 at Bell Labs. Feldman received the 2003 ACM Software System Award for the authoring of this widesprea ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Subroutine
In computer programming, a function or subroutine is a sequence of program instructions that performs a specific task, packaged as a unit. This unit can then be used in programs wherever that particular task should be performed. Functions may be defined within programs, or separately in libraries that can be used by many programs. In different programming languages, a function may be called a routine, subprogram, subroutine, method, or procedure. Technically, these terms all have different definitions, and the nomenclature varies from language to language. The generic umbrella term ''callable unit'' is sometimes used. A function is often coded so that it can be started several times and from several places during one execution of the program, including from other functions, and then branch back (''return'') to the next instruction after the ''call'', once the function's task is done. The idea of a subroutine was initially conceived by John Mauchly during his work on ENIAC, ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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