When to Pass by Reference or Pointer in C : A Guiding Principle?

Passing by Reference or Pointer in C : A Guiding Principle

In C , understanding when to employ passing by reference and when to use pointers is crucial. This practice can lead to efficient and error-free code.

General Situations

• Passing a std::string to a function:

  • foo(std::string*) or foo(std::string&)?

• Passing a tr1::shared_ptr to a function:

  • foo(tr1::shared_ptr* ptr) or foo(tr1::shared_ptr& ptr)?

Pointers vs. References

Passing by reference offers consistency, as every object can be treated as a reference. However, passing by pointer provides the flexibility to handle nullptrs and literals.

Snippet Analysis

The given snippet:

map<string, shared_ptr<vector<string>> > adjacencyMap;
vector<string>* myFriends = new vector<string>();
myFriends->push_back(string("a"));
myFriends->push_back(string("v"));
myFriends->push_back(string("g"));
adjacencyMap["s"] = shared_ptr<vector<string> >(myFriends);

highlights the need to consider the properties of both references and pointers:

• The map keys use references, guaranteeing memory efficiency.
• The vector pointer allows for dynamic allocation, facilitating vector addition.

Rule of Thumb

Ultimately, the appropriate choice depends on the specific requirements. As a guiding principle, consider:

• Use references: For efficient memory usage and when you have guaranteed access to the referenced object.
• Use pointers: When handling nullptrs, working with dynamic memory, or when you need to modify references themselves.

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