CODEWITHSUNDEEP
c++vector
kryptobs2000
kryptobs2000

Reputation: 3537

Can't understand why I'm not being allowed to subscript this vector

The code I'm trying to run:

std::string genBlankName(std::vector<Post> &posts)
{
    std::string baseName = "New Post ";
    int postNum = 1;

    for (std::vector<Post>::iterator currentPost = posts.begin(); currentPost != posts.end(); currentPost++)
    {
        if (posts[currentPost].name.substr(0, baseName.length()) == baseName &&
            utils::is_num(posts[currentPost].name.substr(baseName.length(), std::string::npos)) &&
            utils::to_int(posts[currentPost].name.substr(baseName.length(), std::string::npos)) > postNum)
        {
            postNum = utils::to_int(posts[currentPost].name.substr(baseName.length(), std::string::npos));
        }
    }

    return baseName + utils::to_string(postNum);
}

And the error I get:

/home/brett/projects/CLPoster/CLPoster-build-desktop/../CLPoster/item.h:240: error: no matching function for call to std::vector<cl::Post, std::allocator<cl::Post> >::at(__gnu_cxx::__normal_iterator<cl::Post*, std::vector<cl::Post, std::allocator<cl::Post> > >&)

Sorry for not saying more, but I'm assuming this is a pretty common thing I'm just unaware of being a nub. I'd google it, but it seems too general of a problem to turn up anything useful as I suspect it's more of a problem with my implementation or something along those lines.

Upvotes: 2

Views: 313

Answers (4)

Xeo
Xeo

Reputation: 131829

You don't use iterators on subscripts. Just take a size_t

for (size_t currentPost = 0; currentPost < posts.size(); ++currentPost)

Or dereference the iterator:

currentPost->name.substr(0, baseName.length())

Upvotes: 6

yasouser
yasouser

Reputation: 5187

vector operator[] takes size_type as parameter and not std::vector::iterator type.

Upvotes: 1

user405725
user405725

Reputation:

std::vector<typename T> is a random access container, however, you have to use offset to access elements at given positions. For example, if you want to get element number five, you write something like:

std::vector<int> data;
data[5] = 10;

But in your example you are using iterator. Think of iterator as a pointer to your Post object. You cannot use that pointer as an index of element in your vector. So your code should look like this instead:

std::string genBlankName (std::vector<Post> &posts)
{
    std::string baseName = "New Post ";
    int postNum = 1;

    for (std::vector<Post>::iterator currentPost = posts.begin();
         currentPost != posts.end(); currentPost++)
    {
        if (currentPost->name.substr(0, baseName.length()) == baseName &&
            utils::is_num(currentPost->name.substr(baseName.length(), std::string::npos)) &&
            utils::to_int(currentPost->name.substr(baseName.length(), std::string::npos)) > postNum)
        {
            postNum = utils::to_int(currentPost->name.substr(baseName.length(), std::string::npos));
        }
    }

    return baseName + utils::to_string(postNum);
}

Or you can use indexes, but then you cannot use iterators, for example:

std::string genBlankName (std::vector<Post> &posts)
{
    std::string baseName = "New Post ";
    int postNum = 1;

    for (size_t currentPost = 0; currentPost < posts.size (); ++currentPost)
    {
        if (posts[currentPost].name.substr(0, baseName.length()) == baseName &&
            utils::is_num(posts[currentPost].name.substr(baseName.length(), std::string::npos)) &&
            utils::to_int(posts[currentPost].name.substr(baseName.length(), std::string::npos)) > postNum)
        {
            postNum = utils::to_int(posts[currentPost].name.substr(baseName.length(), std::string::npos));
        }
    }

    return baseName + utils::to_string(postNum);
}

Hope it helps. Happy coding!

Upvotes: 1

Konrad Rudolph
Konrad Rudolph

Reputation: 545923

Subscripting requires the use of an index, you’re using iterators.

You don’t need subscript at all, just dereference your iterator:

currentPost->name.substr(0, baseName.length())

… and so on.

Upvotes: 9

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