Inline function

In the <a href="/facts/C_/Ky2No763">C</a> and <a href="/facts/C%2B%2B/Et0F2qn9">C++</a> <a href="/facts/Programming_language/cWTYbgWa">programming languages</a>, an inline function is one qualified with the <a href="/facts/Keyword_(computer_programming)/pHDlUUgY">keyword</a> inline; this serves two purposes:

<ol><li>It serves as a <a href="/facts/Compiler_directive/RsozxGG0">compiler directive</a> that suggests (but does not require) that the <a href="/facts/Compiler/WNfCDFJe">compiler</a> substitute the body of the function inline by performing <a href="/facts/Inline_expansion/jhQsJwLX">inline expansion</a>, i.e. by inserting the function code at the address of each function call, thereby saving the overhead of a function call. In this respect it is analogous to the register <a href="/facts/Storage_class_specifier/DB1393sn">storage class specifier</a>, which similarly provides an optimization hint.</li>
<li>The second purpose of inline is to change linkage behavior; the details of this are complicated. This is necessary due to the C/C++ separate compilation + linkage model, specifically because the definition (body) of the function must be duplicated in all <a href="/facts/Translation_unit_(programming)/7GbSbEYL">translation units</a> where it is used, to allow inlining during compiling, which, if the function has external <a href="/facts/Linkage_(software)/nlhvu7Rr">linkage</a>, causes a collision during linking (it violates uniqueness of external symbols). C and C++ (and dialects such as GNU C and Visual C++) resolve this in different ways.</li></ol>

Inline function open-in-new

Inline function