Advantages. By inlining your code where it is needed, your program will spend less time in the function call and return parts. It is supposed to make your code go faster, even as it goes larger (see below).
Inlining trivial accessors could be an example of effective inlining. By marking it as inline, you can put a function definition in a header file (i.e. It can be included in multiple compilation unit, without the linker complaining) Disadvantages. It can make your code larger (i.e. If you use inline for non-trivial functions). As such, it could provoke paging and defeat optimizations from the compiler.
It slightly breaks your encapsulation because it exposes the internal of your object processing (but then, every 'private' member would, too). This means you must not use inlining in a PImpl pattern.
It slightly breaks your encapsulation 2: C inlining is resolved at compile time. Which means that should you change the code of the inlined function, you would need to recompile all the code using it to be sure it will be updated (for the same reason, I avoid default values for function parameters). When used in a header, it makes your header file larger, and thus, will dilute interesting informations (like the list of a class methods) with code the user don't care about (this is the reason that I declare inlined functions inside a class, but will define it in an header after the class body, and never inside the class body).
Inlining Magic. The compiler may or may not inline the functions you marked as inline; it may also decide to inline functions not marked as inline at compilation or linking time. Inline works like a copy/paste controlled by the compiler, which is quite different from a pre-processor macro: The macro will be forcibly inlined, will pollute all the namespaces and code, won't be easily debuggable, and will be done even if the compiler would have ruled it as inefficient. Every method of a class defined inside the body of the class itself is considered as 'inlined' (even if the compiler can still decide to not inline it. Virtual methods are not supposed to be inlinable. Still, sometimes, when the compiler can know for sure the type of the object (i.e. The object was declared and constructed inside the same function body), even a virtual function will be inlined because the compiler knows exactly the type of the object.
Template methods/functions are not always inlined (their presence in an header will not make them automatically inline). The next step after 'inline' is template metaprograming. By 'inlining' your code at compile time, sometimes, the compiler can deduce the final result of a function. So a complex algorithm can sometimes be reduced to a kind of return 42; statement.
This is for me extreme inlining. It happens rarely in real life, it makes compilation time longer, will not bloat your code, and will make your code faster.
But like the grail, don't try to apply it everywhere because most processing cannot be resolved this way. Still, this is cool anyway.:-p.
@PravasiMeet: It's C. Let's say you deliver a DLL/shared library to a client, who compiles against it. The inline function foo, using member variable X and doing work Y will get inlined in the client's code. Let's say to need to deliver an updated version of your DLL where you changed the member variable to Z, and add a work YY in addition to work Y. The client just copies the DLL into their project, and BOOM, because the code of foo in their binary is not the updated code you wrote.
Despite the client not having legal access to your private code, inlining makes it quite 'public'. – Sep 7 '15 at 8:38. @KonradRudolph In n4594 I see: 3.2/6: There can be more than one definition of. inline function with external linkage. non-static function template.
C++ Program Using Inline Function
At 5.1.5/6 For a generic lambda, the closure type has a public inline function call operator member template. And at 7.1.2/2: the use of inline keyword is to declare an inline function where it is a suggestion to inline the function body at point of call. So, I conclude that even if they can behave the same, inline functions and function templates are still separate, orthogonal notions that can be mixed (ie inline function template) – Jul 10 '16 at 10:08.
Inlining is a suggestion to the compiler which it is free to ignore. It's ideal for small bits of code.
If your function is inlined, it's basically inserted in the code where the function call is made to it, rather than actually calling a separate function. This can assist with speed as you don't have to do the actual call. It also assists CPUs with pipelining as they don't have to reload the pipeline with new instructions caused by a call. The only disadvantage is possible increased binary size but, as long as the functions are small, this won't matter too much. I tend to leave these sorts of decisions to the compilers nowadays (well, the smart ones anyway).
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The people who wrote them tend to have far more detailed knowledge of the underlying architectures. Inline function is the optimization technique used by the compilers. One can simply prepend inline keyword to function prototype to make a function inline. Inline function instruct compiler to insert complete body of the function wherever that function got used in code. It does not require function calling overhead. It also save overhead of variables push/pop on the stack, while function calling. It also save overhead of return call from a function.
It increases locality of reference by utilizing instruction cache. After in-lining compiler can also apply intra-procedural optimization if specified.
Inno setup kill process before install. I’m having an issue with ‘Retry’. When I click it, even though I have exited the process I was checking for, it still shows in the list and I am unable to continue with setup. If I exit setup and re-run, I can continue on fine.
This is the most important one, in this way compiler can now focus on dead code elimination, can give more stress on branch prediction, induction variable elimination etc. To check more about it one can follow this link. I'd like to add that inline functions are crucial when you are building shared library.
Without marking function inline, it will be exported into the library in the binary form. It will be also present in the symbols table, if exported. On the other side, inlined functions are not exported, neither to the library binaries nor to the symbols table. It may be critical when library is intended to be loaded at runtime. It may also hit binary-compatible-aware libraries.
In such cases don't use inline. Generally speaking, these days with any modern compiler worrying about inlining anything is pretty much a waste of time. The compiler should actually optimize all of these considerations for you through its own analysis of the code and your specification of the optimization flags passed to the compiler. If you care about speed, tell the compiler to optimize for speed.
If you care about space, tell the compiler to optimize for space. As another answer alluded to, a decent compiler will even inline automatically if it really makes sense. Also, as others have stated, using inline does not guarantee inline of anything. If you want to guarantee it, you will have to define a macro instead of an inline function to do it.
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When to inline and/or define a macro to force inclusion? - Only when you have a demonstrated and necessary proven increase in speed for a critical section of code that is known to have an affect on the overall performance of the application. If you care about space, tell the compiler to optimize for space - telling the compiler to optimize for speed can result in smaller binaries with C and C. Similarly, telling the compiler to optimize for space can result in faster execution. Iow, these features don't always work as advertised.
Humans have the ability to understand some aspects of their their program better than a compiler's generalized interpretations (which must also remain usably fast). Human intervention doesn't have to be a bad thing.
– Jul 15 '13 at 21:58. Why not make all functions inline by default? Because it's an engineering trade off. There are at least two types of 'optimization': speeding up the program and reducing the size (memory footprint) of the program.
Inlining generally speeds things up. It gets rid of the function call overhead, avoiding pushing then pulling parameters from the stack.
However, it also makes the memory footprint of the program bigger, because every function call must now be replaced with the full code of the function. To make things even more complicated, remember that the CPU stores frequently used chunks of memory in a cache on the CPU for ultra-rapid access.
If you make the program's memory image big enough, your program won't be able to use the cache efficiently, and in the worst case inlining could actually slow your program down. To some extent the compiler can calculate what the trade offs are, and may be able to make better decisions than you can, just looking at the source code. Conclusion from here: Are there any drawbacks with inline functions? Apparently, There is nothing wrong with using inline functions.
But it is worth noting the following points!. Overuse of inlining can actually make programs slower. Depending on a function's size, inlining it can cause the code size to increase or decrease. Inlining a very small accessor function will usually decrease code size while inlining a very large function can dramatically increase code size.
On modern processors smaller code usually runs faster due to better use of the instruction cache. The speed benefits of inline functions tend to diminish as the function grows in size. At some point the overhead of the function call becomes small compared to the execution of the function body, and the benefit is lost. There are few situations where an inline function may not work:.
For a function returning values; if a return statement exists. For a function not returning any values; if a loop, switch or goto statement exists. If a function is recursive. The inline keyword causes a function to be inlined only if you specify the optimize option.
If optimize is specified, whether or not inline is honored depends on the setting of the inline optimizer option. By default, the inline option is in effect whenever the optimizer is run. If you specify optimize, you must also specify the noinline option if you want the inline keyword to be ignored.
» C Inline Functions An inline function is a function that is expended in line when it is invoked, that is the compiler replaces the function call with the corresponding function code. It is the optimization technique used by the compilers. One can simply prepend inline keyword to function prototype to make a function inline. Inline function instruct compiler to insert complete body of the function wherever that function got used in code. Remember that inline keyword merely sends the request, not a command to the compiler, the compiler may ignore this request if the function definition is too long or too complicated and compile the function as a normal function. Advantages. It avoids the overhead of calling the actual function.
This is because the complier performs and inline expansion which eliminates the time overhead when a function is called. Reduces space as no separate set of instructions in memory is written. Using inline, you can put a function definition in a header file (i.e. It can be included in multiple compilation unit, without the linker complaining.) Some situations where inline expansion may not work, they are:. If function returning some values and a loop, a switch or a goto exists.
If function return type is void and a return statement is exists. If function contains any static variable. If inline function is recursive.
The inline and inline specifiers instruct the compiler to insert a copy of the function body into each place the function is called. The insertion (called inline expansion or inlining) occurs only if the compiler's cost/benefit analysis show it to be profitable. Inline expansion alleviates the function-call overhead at the potential cost of larger code size. The forceinline keyword overrides the cost/benefit analysis and relies on the judgment of the programmer instead. Exercise caution when using forceinline. Indiscriminate use of forceinline can result in larger code with only marginal performance gains or, in some cases, even performance losses (due to increased paging of a larger executable, for example).
Using inline functions can make your program faster because they eliminate the overhead associated with function calls. Functions expanded inline are subject to code optimizations not available to normal functions. The compiler treats the inline expansion options and keywords as suggestions. There is no guarantee that functions will be inlined. You cannot force the compiler to inline a particular function, even with the forceinline keyword. When compiling with /clr, the compiler will not inline a function if there are security attributes applied to the function.
The inline keyword is available only in C. The inline and forceinline keywords are available in both C and C. For compatibility with previous versions, inline is a synonym for inline. The inline keyword tells the compiler that inline expansion is preferred.
However, the compiler can create a separate instance of the function (instantiate) and create standard calling linkages instead of inserting the code inline. Two cases where this can happen are:. Recursive functions. Functions that are referred to through a pointer elsewhere in the translation unit.
These reasons may interfere with inlining, as may others, at the discretion of the compiler; you should not depend on the inline specifier to cause a function to be inlined. As with normal functions, there is no defined order of evaluation of the arguments to an inline function. In fact, it could be different from the order in which the arguments are evaluated when passed using normal function call protocol. The compiler optimization option helps to determine whether inline function expansion actually occurs. Performs cross-module inlining regardless of whether it was requested in source code. Although inline functions are similar to macros (because the function code is expanded at the point of the call at compile time), inline functions are parsed by the compiler, whereas macros are expanded by the preprocessor.
As a result, there are several important differences:. Inline functions follow all the protocols of type safety enforced on normal functions. Inline functions are specified using the same syntax as any other function except that they include the inline keyword in the function declaration. Expressions passed as arguments to inline functions are evaluated once. In some cases, expressions passed as arguments to macros can be evaluated more than once. The following example shows a macro that converts lowercase letters to uppercase.
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