Undefined Reference To Inline Function Update

An “undefined reference” error typically occurs when a function is declared but not defined in the program. However, when an inline function is involved, there may be additional causes of this error.

When a function is declared as inline in C or C++, the compiler may choose to replace the function call with the actual function code during the compilation process, instead of generating a separate function code that would be called at runtime. This optimization can improve program performance, but it also means that the function definition must be visible to all translation units that use it.

Therefore, if you have an inline function declared in a header file and included in multiple source files, you need to make sure that the function definition is also included in each source file that uses the function. Otherwise, you may get an “undefined reference” error during linking, because the compiler cannot find the actual function code to substitute for the function call.

To resolve this error, you can either move the inline function definition from the header file to a source file and compile it separately, or you can include the function definition in each source file that uses the function.

“extern inline” is a keyword combination in C and C++ programming languages that is used to define a function that can be inlined by the compiler if deemed appropriate, but also allows the function to be separately compiled and linked with other code.

The “extern” keyword indicates that the function is defined externally, i.e., its implementation may be in another source file. This is necessary because if a function is defined as inline, the compiler will usually include its code directly in the calling function, but if the function is defined in another file, the compiler must generate a separate function that can be linked to the calling function.

The “inline” keyword suggests to the compiler that the function should be inlined, i.e., the code of the function should be substituted directly into the calling function rather than calling the function at runtime. This can result in faster code execution, but it may also increase the size of the binary executable file.

The combination of “extern inline” allows the function to be inlined if possible, but still provides a separate implementation that can be linked to the calling function if necessary.

An inline function in a C file is a function that is defined with the inline keyword, which suggests to the compiler to insert the function’s code directly into the calling code rather than calling the function. This can lead to improved performance by reducing function call overhead and allowing the compiler to optimize the code more effectively.

To define an inline function in a C file, you can use the inline keyword before the function definition. Here’s an example:

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

In this example, the add function is defined as an inline function. When this function is called in the code, the compiler will replace the function call with the actual code of the function, which can lead to faster code execution.

It’s worth noting that the inline keyword is a suggestion to the compiler and not a requirement. The compiler may choose not to inline the function if it deems it inappropriate or if it cannot determine the benefit of inlining the function. Additionally, some compilers may automatically inline small functions even if they are not explicitly marked as inline.