What is C++ Inline Functions?

What is C++ Inline Functions?

C++ gives an inline function to diminish the function call overhead. Inline functions in C++ are a function that is extended in line when it is called. When the inline work is called, the entire code of the inline work gets embedded or subbed at the place of the inline work call. This replacement performs by the C++ compiler at arranging time. Inline functions might build proficiency in case it is little.

The compiler can overlook the solicitation for inlining. C++ inline function is an influential idea that regularly utilizes with classes. If a function is inline, the compiler puts a duplicate of the code of that capacity at each point; where the function is called at order time. 

The compiler can disregard the inline qualifier on the off chance that characterized work is more than a line. A function definition in a class definition is an inline work definition, even without the utilization of the inline specifier.


Inline return-type function-name(parameters)




A compiler may not perform inlining in such conditions like: 

  • If a function contains a circle. (for, while, do-while) 
  • If a function contains static factors. 
  • If a function is recursive. 
  • Also, If the function’s return type is other than void, and the return proclamation doesn’t exist in the function body. 
  • If a function contains a switch or goes to articulation. 

inline functions in C++ have the following benefits: 

  • Function call overhead doesn’t happen. 
  • It likewise saves the overhead of push/pop factors on the stack when capacity is called. 
  • It additionally saves the overhead of a return call from a capacity. 
  • When you inline a function, you might empower the compiler to perform setting explicit advancement on the group of capacity. Such enhancements are impractical for ordinary capacity calls. Different improvements can be gotten by thinking about the progressions of the calling setting and the called setting. 
  • Inline functions might be helpful (in case it is little) for installed frameworks because inline can yield less code than the functions call introduction and return. 

Inline functions and classes: 

It is likewise conceivable to characterize the inline work inside the class. Every one of the functions characterized inside the class is verifiably inline. Consequently, every one of the limitations of inline functions is additionally applied here. On the off chance that you need to unequivocally announce inline functions in the class, simply pronounce the functions inside the class and characterize them outside the class utilizing the inline keyword. 

C++ compiler checks the contention of inline functions, and vital changes are performed accurately. A preprocessor full scale isn’t competent for doing this. Something else is that the macros are overseen by the preprocessor and inline capacities are overseen by the C++ compiler. 

Without a doubt, every one of the capacities characterized inside the class is certainly inline, and the C++ compiler will perform inline calls of these functions. However, the C++ compiler can’t perform inlining if the functions are virtual.

It is simply valuable to make the functions inline if the time spent during a capacity call is more contrasted with the body of the function execution time. The inlining of the show() work is of restricted worth because the measure of time the I/O articulation will take far surpasses the overhead of a function call. 

Implementation of inline functions in C++

At the point when the program executes the capacity, consider guidance the CPU stores the memory address of the guidance following the capacity call, duplicates the contentions of the capacity on the stack, and moves control to the predetermined capacity. The CPU then, at that point, executes the capacity code, stores the capacity return esteem in a predefined memory area/register, and returns control to the calling capacity.

This can turn out to be overhead if the execution season of capacity is not exactly the changing time from the guest capacity to called work (callee). For capacities that are enormous as well as perform complex errands; the overhead of the capacity call is generally unimportant; contrasted with the measure of time the capacity takes to run.

In any case, for little, normally utilized capacities; the time expected to settle on the capacity decision is regularly much excess of executing the capacity’s code. This overhead happens for little capacities since the execution season of little capacity is not exactly the exchanging time.

Purpose of inline functions in C++

The answer for this issue is to utilize large-scale definitions known as macros. The preprocessor macros are broadly utilized in C. However, the significant disadvantage with the macros is that these are not typical functions, which implies the mistake-checking interaction won’t be finished during the arrangement. 

C++ has given one answer for this issue. On account of function calls, the ideal opportunity for calling such little functions is enormous. At the point when the function is experiencing inside the main() technique, its extension with its definition, consequently saving time.

We can’t give the inlining to the capacities in the accompanying conditions

  • On the off chance that a function is recursive. 
  • A function contains a circle like for, while, do-while circle. 
  • Also, A function contains static factors. 
  • A function contains a switch or goes to articulation.

When do we require an inline function? 

An inline function can be utilized in the accompanying situations: 

  • An inline function can be utilized when the exhibition is required. 
  • It tends to be utilized over the macros. 
  • We can utilize the inline function outside the class so we can conceal the inner execution of the function.

The last thing to remember is that inline functions are an important component of C++. Suitable utilization of inline functions can give execution improvement; however assuming inline capacities are utilized self-assertively, they can’t give a better outcome. All in all, don’t anticipate better execution of a program. Try not to make each function inline. It is smarter to keep inline functions as little as could be expected.

Disadvantages of inline functions in C++

Following are some of the disadvantages of inline functions in C++: 

  • The factors that are made inside the inline capacity will burn through extra registers. If the factors increment, the utilization of registers likewise builds, which might expand the overhead on register variable asset usage. It implies that when the capacity call is supplanted with an inline work body, then, at that point the quantity of factors additionally expands, prompting an expansion in the number of registers. This causes an overhead on asset usage. 
  • If we utilize numerous inline capacities, the twofold executable record likewise turns out to be enormous. 
  • The utilization of so many inline capacities can diminish the guidance store hit rate, lessening the speed of guidance brought from the reserved memory to that of the essential memory. 
  • Now and then inline capacities are not valuable for some implanted frameworks because; at times, the size of the inserted is considered more significant than the speed. 
  • It can likewise cause whipping because of the increment in the size of the paired executable record. If the whipping happens in the memory, it prompts the error in the presentation of the computer.

Example of inline functions in C++


#include <iostream>

using namespace std;

inline void num(int nb)


                cout  << nb << endl;


Int main()


                num(9);  // function number: 1

                num(3);  // function number: 2

                num(111);  // function number: 3

                return 0;






Hope this article helps you a lot in understanding inline functions in C++. If you’re interested in free online courses with certificates, So enroll today on Great Learning Programme

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