Convert pugixml's result.offset to column/line

Question

I need user-friendly error reporting for an application that uses pugixml.
I am currently using result.offset.
Is there a way to get the line and column instead? I am potentially dealing with large XML files, if that makes a difference.

Answer 1

This functionality is not readily available in pugixml since it's relatively expensive to do it on every parse, and after parsing is complete it's impossible to recover file/line information in the general case.

Here's a snippet that builds an offset -> line mapping that you can use in case parsing fails or you need the information for other reasons; feel free to tweak file I/O code to match your requirements.

typedef std::vector<ptrdiff_t> offset_data_t;

bool build_offset_data(offset_data_t& result, const char* file)
{
    FILE* f = fopen(file, "rb");
    if (!f) return false;

    ptrdiff_t offset = 0;

    char buffer[1024];
    size_t size;

    while ((size = fread(buffer, 1, sizeof(buffer), f)) > 0)
    {
    for (size_t i = 0; i < size; ++i)
        if (buffer[i] == '\n')
            result.push_back(offset + i);

    offset += size;
    }

    fclose(f);

    return true;
}

std::pair<int, int> get_location(const offset_data_t& data, ptrdiff_t offset)
{
    offset_data_t::const_iterator it = std::lower_bound(data.begin(), data.end(), offset);
    size_t index = it - data.begin();

    return std::make_pair(1 + index, index == 0 ? offset + 1 : offset - data[index - 1]);
}