In programming, a gotcha is a valid construct in a system, program or programming language that works as documented but is counter-intuitive and almost invites mistakes because it is both easy to invoke and unexpected or unreasonable in its outcome. [1]
The classic gotcha in C/C++ is the construct
if(a=b)code;
It is syntactically valid: it puts the value of b
into a
and then executes code
if a
is non-zero. Sometimes this is even intended. However most commonly it is a typo: the programmer probably meant
if(a==b)code;
which executes code
if a
and b
are equal. [1] Modern compilers will usually generate a warning when encountering the former construct (conditional branch on assignment, not comparison), depending on compiler options (e.g., the -Wall
option for gcc). To avoid this gotcha, there is a recommendation [2] to keep the constants in the left side of the comparison, e.g. 42 == x
rather than x == 42
. This way, using =
instead of ==
will cause a compiler error (see Yoda conditions). Many kinds of gotchas are not detected by compilers, however.[ citation needed ]
In computer programming, assembly language, is any low-level programming language in which there is a very strong correspondence between the instructions in the language and the architecture's machine code instructions. Assembly language usually has one statement per machine instruction (1:1), but constants, comments, assembler directives, symbolic labels of, e.g., memory locations, registers, and macros are generally also supported.
C is a general-purpose computer programming language. It was created in the 1970s by Dennis Ritchie, and remains very widely used and influential. By design, C's features cleanly reflect the capabilities of the targeted CPUs. It has found lasting use in operating systems, device drivers, protocol stacks, though decreasingly for application software, and is common in computer architectures that range from the largest supercomputers to the smallest microcontrollers and embedded systems.
PL/I is a procedural, imperative computer programming language developed and published by IBM. It is designed for scientific, engineering, business and system programming. It has been used by academic, commercial and industrial organizations since it was introduced in the 1960s, and is still used.
In computing, an optimizing compiler is a compiler that tries to minimize or maximize some attributes of an executable computer program. Common requirements are to minimize a program's execution time, memory footprint, storage size, and power consumption.
Java and C++ are two prominent object-oriented programming languages. By many language popularity metrics, the two languages have dominated object-oriented and high-performance software development for much of the 21st century, and are often directly compared and contrasted. Java appeared about 10 years later and its syntax was based on C/C++.
Generic programming is a style of computer programming in which algorithms are written in terms of types to-be-specified-later that are then instantiated when needed for specific types provided as parameters. This approach, pioneered by the ML programming language in 1973, permits writing common functions or types that differ only in the set of types on which they operate when used, thus reducing duplication. Such software entities are known as generics in Ada, C#, Delphi, Eiffel, F#, Java, Nim, Python, Go, Rust, Swift, TypeScript and Visual Basic .NET. They are known as parametric polymorphism in ML, Scala, Julia, and Haskell ; templates in C++ and D; and parameterized types in the influential 1994 book Design Patterns.
In programming languages, a type system is a logical system comprising a set of rules that assigns a property called a type to the various constructs of a computer program, such as variables, expressions, functions or modules. These types formalize and enforce the otherwise implicit categories the programmer uses for algebraic data types, data structures, or other components. The main purpose of a type system is to reduce possibilities for bugs in computer programs by defining interfaces between different parts of a computer program, and then checking that the parts have been connected in a consistent way. This checking can happen statically, dynamically, or as a combination of both. Type systems have other purposes as well, such as expressing business rules, enabling certain compiler optimizations, allowing for multiple dispatch, providing a form of documentation, etc.
In computing, inline expansion, or inlining, is a manual or compiler optimization that replaces a function call site with the body of the called function. Inline expansion is similar to macro expansion, but occurs during compilation, without changing the source code, while macro expansion occurs prior to compilation, and results in different text that is then processed by the compiler.
In computer programming, specifically when using the imperative programming paradigm, an assertion is a predicate connected to a point in the program, that always should evaluate to true at that point in code execution. Assertions can help a programmer read the code, help a compiler compile it, or help the program detect its own defects.
In computer programming, an assignment statement sets and/or re-sets the value stored in the storage location(s) denoted by a variable name; in other words, it copies a value into the variable. In most imperative programming languages, the assignment statement is a fundamental construct.
In computer programming, the term magic number has multiple meanings. It could refer to one or more of the following:
ALGOL 68 is an imperative programming language that was conceived as a successor to the ALGOL 60 programming language, designed with the goal of a much wider scope of application and more rigorously defined syntax and semantics.
Short-circuit evaluation, minimal evaluation, or McCarthy evaluation is the semantics of some Boolean operators in some programming languages in which the second argument is executed or evaluated only if the first argument does not suffice to determine the value of the expression: when the first argument of the AND
function evaluates to false
, the overall value must be false
; and when the first argument of the OR
function evaluates to true
, the overall value must be true
.
High Level Assembly (HLA) is a high-level assembly language developed by Randall Hyde. It allows the use of higher-level language constructs to aid both beginners and advanced assembly developers. It fully supports advanced data types and object-oriented programming. It uses a syntax loosely based on several high-level programming languages (HLLs), such as Pascal, Ada, Modula-2, and C++, to allow creating readable assembly language programs, and to allow HLL programmers to learn HLA as fast as possible.
In computer programming, operators are constructs defined within programming languages which behave generally like functions, but which differ syntactically or semantically.
In computer science, a relational operator is a programming language construct or operator that tests or defines some kind of relation between two entities. These include numerical equality and inequalities.
The computer programming languages C and Pascal have similar times of origin, influences, and purposes. Both were used to design their own compilers early in their lifetimes. The original Pascal definition appeared in 1969 and a first compiler in 1970. The first version of C appeared in 1972.
In computer science, the syntax of a computer language is the set of rules that defines the combinations of symbols that are considered to be correctly structured statements or expressions in that language. This applies both to programming languages, where the document represents source code, and to markup languages, where the document represents data.
Interprocedural optimization (IPO) is a collection of compiler techniques used in computer programming to improve performance in programs containing many frequently used functions of small or medium length. IPO differs from other compiler optimizations because it analyzes the entire program; other optimizations look at only a single function, or even a single block of code.
In computer programming, a comment is a programmer-readable explanation or annotation in the source code of a computer program. They are added with the purpose of making the source code easier for humans to understand, and are generally ignored by compilers and interpreters. The syntax of comments in various programming languages varies considerably.
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