Introduction / Context:
The One Definition Rule (ODR) in C++ governs how many definitions of an entity (functions, objects, types) may appear in a program. Violating the ODR often leads to linker errors or undefined behavior. This question asks whether you may define the same (non-inline) function more than once in the same program.
Given Data / Assumptions:
- We are discussing ordinary (non-inline, non-template, non-special) functions.
- Multiple translation units are linked together to form one program.
- Header inclusion may replicate declarations, but not definitions, unless special rules apply.
Concept / Approach:
- Under the ODR, each function must have exactly one definition in the entire program (inline functions and templates have special rules).
- Multiple identical definitions of a non-inline function across translation units violate the ODR.
- Correct practice: place the function definition in a single .cpp file and declare it in headers with extern linkage as needed.
Step-by-Step Solution:
Identify entity: non-inline function.Apply ODR: only one definition is permitted in the program.Therefore, the correct answer states that multiple definitions are not allowed.
Verification / Alternative check:
Creating two .cpp files each defining the same function foo() leads to ”multiple definition” linker errors on most toolchains.
Why Other Options Are Wrong:
- Identical definitions / separate includes / repeated includes: All still produce multiple definitions unless the function is marked inline or is a template defined consistently, which is not the case stated.
- None of the above: Incorrect because the ODR prohibition applies.
Common Pitfalls:
- Placing non-inline function definitions in headers and including them in multiple translation units.
- Confusing declarations (allowed in many places) with definitions (must be unique).
Final Answer:
C++ does not allow you to define the same functions more than once in the same program
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