How to pass a vector to a function in C ? (By Reference)

To pass a vector by reference in C , use std::vector& for modification or const std::vector& for read-only access—avoiding copies, enabling direct changes, and ensuring efficiency and safety.

To pass a vector to a function by reference in C , you declare the parameter as std::vector<t>&amp;amp;</t> — not std::vector<t></t> (which copies) or std::vector<t>*</t> (which uses a pointer). This avoids copying all elements and lets the function modify the original vector directly.

Declare the parameter as a non-const lvalue reference

Use std::vector<int>&amp;amp;</int> (or whatever type) if the function needs to change the vector — e.g., add, remove, or update elements.

• Inside the function, operations like v.push_back(42) or v[0] = 99 affect the original vector.
• No extra memory is allocated for the vector data — only the reference itself (typically pointer-sized) is passed.

Prefer const reference when you only read the vector

If the function only inspects the vector (e.g., computes sum or finds max), use const std::vector<t>&amp;amp;</t>.

• This prevents accidental modification and signals intent clearly.
• Still avoids copying — just as efficient as non-const reference.
• Allows calling the function with temporaries or const vectors.

Don’t forget to include and use std::

Make sure your code includes the header and properly scopes the type:

• #include <vector></vector>
• Either write std::vector<double>&amp;amp; v</double>, or use using std::vector; (not using namespace std; in headers).

Avoid common pitfalls

Two mistakes beginners often make:

• Passing by value (std::vector<int> v</int>) — silently copies everything, which is slow for large vectors.
• Using raw pointers unnecessarily — std::vector<int>* v</int> adds indirection and null-checking overhead without benefit.
• Returning a reference to a local vector — that’s undefined behavior.

Basically just match the reference type to your intent: & for modification, const& for reading — and you’re good.

The above is the detailed content of How to pass a vector to a function in C ? (By Reference). For more information, please follow other related articles on the PHP Chinese website!