调整vector大小时出现“no matching constructor”错误求助

Hey there, let's break down why you're hitting this error and how to fix it step by step.

First, Fix the Incomplete Copy Constructor #

Looking at your code, your copy constructor definition is cut off and has a syntax error:

Foo::Foo( const Foo& other) { name_ = other.name(); score_ = other.score(...

You need to complete the call to score() and close the function. A cleaner, more efficient version using an initializer list (instead of in-body assignment) would be:

Foo::Foo(const Foo& other) : name_(other.name()), score_(other.score()) {}

Root Cause of the Resize Error #

The main issue triggering the "no matching constructor" error during vector resizing is that your Foo class lacks a default constructor (a constructor that takes no parameters).

When you call vector::resize() without providing a pre-made element to copy, the vector needs to create new Foo objects from scratch. To do this, it looks for a default constructor (Foo()), but your class only defines:

• A constructor that takes a string and double
• A copy constructor
• A move constructor

Since the compiler can't find a matching default constructor, it throws the error you're seeing.

Solutions #

You have two solid options to fix this:

Option 1: Add a Default Constructor #

You can explicitly define a default constructor, either with custom initial values or let the compiler generate one for you:

Custom Default Constructor

class Foo {
public:
    // Add this default constructor
    Foo() : name_(""), score_(0.0) {}
    // ... rest of your existing constructors and methods
};

Use Compiler-Generated Default Constructor (C++11+)

If you just want the compiler to generate a default constructor that default-initializes your members, use:

class Foo {
public:
    // Add this line to use compiler-generated default constructor
    Foo() = default;
    // ... rest of your existing constructors and methods
};

Option 2: Resize with a Pre-Defined Foo Object #

If you don't want to add a default constructor, you can pass an existing Foo instance to resize(). The vector will use the copy constructor to create new elements based on this instance:

#include <vector>

int main() {
    std::vector<Foo> fooVector;
    Foo defaultFoo("Default Name", 0.0);
    // Resize to 5 elements, all copies of defaultFoo
    fooVector.resize(5, defaultFoo);
    return 0;
}

Either of these approaches will resolve the "no matching constructor" error when resizing your vector.

内容的提问来源于stack exchange，提问作者Lin Ma