Comparison of the differences between C++ inline functions and macro definitions

Inline functions are expanded at compile time, and macro definitions are replaced during preprocessing. Inline functions: Accept parameters and have a return type. Can access local variables. Performance is better than macro definition. More readable. Macro definition: Do not accept parameters and have no return type. Local variables cannot be accessed. Performance is worse than inline functions. Provide concise syntax and facilitate customization. Documentation

Comparison of the differences between C inline functions and macro definitions

Introduction

In C, inline functions and macro definitions are two important language features used to improve code performance and readability. While they share some similarities, there are also key differences in behavior and usage.

Inline functions

• Inline functions are directly expanded at the call point during compilation, rather than calling a separate function.
• The compiler inlines the function body in the form of a function body instead of generating calling code.
• Inline functions can accept parameters, have a return type, and can contain local variables.
• Inline functions can access local variables at the call site.

Benefits:

• Improved performance due to the elimination of function call overhead.
• Improves readability because the code for inline functions appears directly at the call site.
• Allow inline function optimization, the compiler can inline it.

Grammar:

inline return_type function_name(parameter_list) {
  // 函数体
}

Macro definition

• Macro definition is text replacement, in preprocessing Stage replaces the macro name with the specified text.
• Macro definitions have no parameters, no return type, and cannot access local variables.
• Macro definitions are defined with the #define keyword.

Benefits:

• For simple constants or short fragments of code, macro definitions can provide concise syntax.
• Allows the code to be self-documenting because the macro name can describe its purpose.

Grammar:

#define macro_name replacement_text

Practical case

The following shows how inline functions and macro definitions are actually used of:

Inline function:

inline int square(int x) {
  return x * x;
}

int main() {
  int result = square(5);
  // ...
}

In this example, the square() function is inlined, expanding to # at the call site ##return 5 * 5;.

Macro definition:

#define MAX_VALUE 100

int main() {
  int value = MAX_VALUE;
  // ...
}

In this example,

MAX_VALUE is replaced with the constant 100.

Summary of differences

FeaturesInline functionsMacro definitionReplacement methodExpand during compilationReplace during preprocessingAccept parameters YesNoReturn typeYesNoAccess local variablesYesNoPerformanceHighLowReadabilityHighLow

Selection Criteria

In general, inline functions are recommended for small and performance-critical code that requires parameters, local variables, or return types. Macro definitions, on the other hand, are more suitable for simple constants or code self-documentation.

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