can anyone explain me how to use the inline function in c++ code with example?

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Quick, practical primer (Linux/g++) plus a tiny example and troubleshooting checklist that complements the replies from , and .

The keyword inline in modern C++ mainly affects linkage/definition rules (it allows identical definitions in multiple translation units), and only secondarily serves as an optimization hint — the compiler still decides whether to actually substitute the call. Member functions defined inside a class and constexpr/consteval functions are implicitly inline; C++17 added inline variables for header-only patterns. (en.cppreference.com)

Practical pattern on Linux (g++): put the full function definition in a header so every translation unit sees it. Example header and compile steps:

/* add.hpp */
#ifndef ADD_HPP
#define ADD_HPP

inline int add(int a, int b) { return a + b; }

#endif

Compile with optimization enabled so the compiler will consider inlining at call sites:

g++ -O2 -c main.cpp
g++ -O2 main.o other.o -o app

To give the compiler more inlining freedom use -O3 or -finline-functions (these control GCC's inlining heuristics). (gcc.gnu.org)

If a specific function must be inlined for a measured reason, GCC provides the always_inline function attribute (use with care — forcing inlining can increase code size and hurt cache behavior). To debug why a function was or was not inlined, enable the inlining dumps or opt-info (-fdump-ipa-inline-optimized-missed, -fopt-info-inline) or use the developer/debug options. (gcc.gnu.org)

Troubleshooting checklist (common gotchas):

  • Multiple-definition link errors usually mean the definitions differ or inline was omitted in some TUs; identical definitions are required when they are visible across TUs. (en.cppreference.com)
  • Undefined-reference errors mean the body isn’t visible to the TU that needs it (move the definition into a header or link the TU that contains a non-inline definition).
  • Measure with a profiler before and after inlining — as warned, inlining can hurt as well as help. Remember the macro-vs-function tradeoffs described by when deciding between macros and inline functions.

References: cppreference on inline semantics and C++17 inline variables; GCC docs for optimization and function attributes. (en.cppreference.com)

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use the inline keyword. Note that the compiler can choose not to respect your request.

Thanks for your reply.

The inline functions are complier dependent. But i want to use this inline function in my code. How can i do this in linux?

use the inline keyword. Note that the compiler can choose not to respect your request.

Thanks for your reply.

The inline functions are complier dependent. But i want to use this inline function in my code. How can i do this in linux?

Macro invocations do not perform type checking, or even check that arguments are well-formed, whereas function calls usually do.
In C, a macro cannot use the return keyword with the same meaning as a function would do (it would make the function that asked the expansion terminate, rather than the macro). In other words, you cannot make the macro return something which is not the result of the last expression invoked inside it.

can anyone explain me how to use the inline function in c++ code with example?

There are two ways, actually. The inline keyword is one:

// foo is explicitly inline
inline void foo()
{
    /* ... */
}

Another is for member functions defined inside of a class:

class foo {
public:
    // bar is implicitly inline
    void bar()
    {
        /* ... */
    }
};

But i want to use this inline function in my code.

Why? Inlining involves a cost, and it's a common misconception that there will always be performance improvements. The prevailing advice when it comes to inlining is to avoid it unless you can prove that the benefits outweigh the costs.

Macro invocations do not perform type checking, or even check that arguments are well-formed, whereas function calls usually do.

Preprocessor macros are textual replacements performed prior to compilation. Any type checking and such is performed, just not in a way that's easy to debug. You will[/] get warnings and errors for problematic code, but it's based on the preprocessed code rather than the original source.

In other words, you cannot make the macro return something which is not the result of the last expression invoked inside it.

It gets worse. If you want the macro to have its own scope like a function, you can't return anything at all without using an output variable. This is because the usual tricks for creating a scope don't evaluate to a result that can be used:

#define mymacro() do { \
    // stuff      \
} while(0)

int main()
{
    mymacro();
}

The output variable, while workable, is distinctly less convenient than return values:

#define mymacro(output) do { \
    // stuff        \
    output = result; \
} while(0)

int main()
{
    T rv;

    mymacro(rv);
}

can anyone explain me how to use the inline function in c++ code with example?

Sharing one article for the same
inline article

Above article will help in getting much deeper understanding about it.

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