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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]
Common function undeclared, e.g.: xyz.cpp: In function `int main()': xyz.cpp:6: `cout' undeclared (first use this function) [ 3 ] This means that the programmer most likely forgot to include iostream .
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 .
In the C++ programming language, special member functions [1] are functions which the compiler will automatically generate if they are used, but not declared explicitly by the programmer. The automatically generated special member functions are: Default constructor if no other constructor is explicitly declared.
The C preprocessor (used with C, C++ and in other contexts) defines an include directive as a line that starts #include and is followed by a file specification. COBOL defines an include directive indicated by copy in order to include a copybook. Generally, for C/C++ the include directive is used to include a header file, but can