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In the C and C++ programming languages, unistd.h is the name of the header file that provides access to the POSIX operating system API. [1] It is defined by the POSIX.1 standard, the base of the Single Unix Specification, and should therefore be available in any POSIX-compliant operating system and compiler.
It also provides many built-in functions which can be used to eliminate the need for shell-scripting in the makefile rules as well as to manipulate the variables set and used in the makefile. [17] For example, the foreach function can be used to iterate over a list of values, such as the names of files in a given directory. [18]
The C++ Standard Library provides several generic containers, functions to use and manipulate these containers, function objects, generic strings and streams (including interactive and file I/O), support for some language features, and functions for common tasks such as finding the square root of a number.
Similarly, a variable CPPFLAGS exists with switches to be passed to the C or C++ preprocessor. Similarly, FFLAGS enables the addition of switches for a Fortran compiler. These variables are most commonly used to specify optimization or debugging switches to a compiler, as for example -g , -O2 or ( GCC -specific) -march=athlon .
Statement separator – demarcates the boundary between two statements; need needed for the last statement Line continuation – escapes a newline to continue a statement on the next line Some languages define a special character as a terminator while some, called line-oriented , rely on the newline .
The comma operator separates expressions (which have value) in a way analogous to how the semicolon terminates statements, and sequences of expressions are enclosed in parentheses analogously to how sequences of statements are enclosed in braces: [1] (a, b, c) is a sequence of expressions, separated by commas, which evaluates to the last expression c, while {a; b; c;} is a sequence of ...
Modern C++ compilers are tuned to minimize abstraction penalties arising from heavy use of the STL. The STL was created as the first library of generic algorithms and data structures for C++, with four ideas in mind: generic programming, abstractness without loss of efficiency, the Von Neumann computation model, [2] and value semantics.
The qmake tool helps simplify the build process for development projects across different platforms. It automates the generation of Makefiles so that only a few lines of information are needed to create each Makefile. You can use qmake for any software project, whether it is written with Qt or not.