How can I find an object in a vector based on class properties?

Question

I have a class Attribute with the property std::string attributeName. I would like to develop a simple function that returns the index of the Attribute that has an attributeName matching a provided string. Unfortunate restrictions include: I do not have c++0x at my disposal, and I have already overloaded the Attribute == operator for something more complex. Any help would be appreciated, thanks!

edit- I'm very sorry, I realized it is not clear that there is a vector of attributes I am searching in. vector<Attribute> aVec.

Can there be more than one object with the same attribute value? Do you want a set of results, or the first match? Can the vector be reordered? Is performance important? — Peter Wood, Feb 25 '13 at 09:16

Some programmer dude · Answer 1 · 2013-02-25T09:39:59.393

Use std::find_if with a custom function object:

class FindAttribute
{
    std::string name_;

public:
    FindAttribute(const std::string& name)
        : name_(name)
        {}

    bool operator()(const Attribute& attr)
        { return attr.attributeName == name_; }
};

// ...

std::vector<Attribute> attributes;
std::vector<Attribute>::iterator attr_iter =
    std::find_if(attributes.begin(), attributes.end(),
        FindAttribute("someAttrName"));
if (attr_iter != attributes.end())
{
    // Found the attribute named "someAttrName"
}

To do it in C++11, it actually not that different, except you obviously don't need a function object, or have to declare the iterator type:

std::vector<Attribute> attributes;

// ...

auto attr_iter = std::find_if(std::begin(attributes), std::end(attributes),
    [](const Attribute& attr) -> bool
    { return attr.attributeName == "someAttrName"; });

Or if you need to do this multiple times with different names, create the lambda function as a variable, and use std::bind in the call to std::find_if:

auto attributeFinder =
    [](const Attribute& attr, const std::string& name) -> bool
    { return attr.attributeName == name; };

// ...

using namespace std::placeholders;  // For `_1` below

auto attr_iter = std::find_if(std::begin(attributes), std::end(attributes),
    std::bind(attributeFinder, _1, "someAttrName"));

Could you put the answer how to do it in modern C++, too, for the future? — Peter Wood, Feb 25 '13 at 09:16

score 2 · Answer 2 · answered Feb 06 '16 at 08:00

2

you can simply use a for loop for reaching this purpose:

for (int i = 0; i<aVec.size();i++)
{
    if(aVec[i].attributeName == "yourDesiredString")
    {
        //"i" is the index of your Vector.      
    }
}

answered Feb 06 '16 at 08:00

Mahdi Rashidi

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Maciek B · Answer 3 · 2013-02-25T10:21:32.920

You can also use bind function from boost library:

std::vector<Attribute>::iterator it = std::find_if(
     aVec.begin(),
     aVec.end(),
     boost::bind(&Attribute::attributeName, _1) == "someValue"
);

or C++11 bind function:

std::vector<Attribute>::iterator it = std::find_if(
    aVec.begin(),
    aVec.end(),
    std::bind(
        std::equal_to<std::string>(),
        std::bind(&Attribute::attributeName, _1),
        "someValue"
    )
);

without declaring the predicate class or function

How can I find an object in a vector based on class properties?

3 Answers3

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