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From:Warren Young Date:February 14 2005 3:34pm
Subject:Re: [patch] BadFieldName exception
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Chris Frey wrote:

> In the interests of code correctness and safety, here is a patch for a new
> exception: BadFieldName.  

Accepted, with modifications detailed below.

> +  std::vector<std::string> known_fields;

Elided.  First, exceptions are frequently copied on throw, so you don't 
want exception objects to be unnecessarily large; one can get that list 
another way.  Second, it isn't the purpose of an exception object to 
help the C++ program recover, but simply to flag an error, which the 
programmer/user must cope with.

> +//: Exception thrown when lookup_by_name can't find the specified field.
> +class BadFieldName {
> +public:
> +  std::string bad_field;
> +  std::vector<std::string> known_fields;
> +
> +  BadFieldName(const char *bad, const std::vector<std::string> &names)
> +    : bad_field(bad), known_fields(names) {}
> +};

I changed this to be more like the other BadFieldName class, and like 
the other exceptions: its member is called 'error' now, and it holds a 
constructed error message, not just the field name.

>  const ColData Row::lookup_by_name(const char* i) const
>  {
> -	return (*this)[res->field_num(std::string(i))];
> +	int si = res->field_num(std::string(i));
> +	if( si >= res->num_fields() )
> +		throw BadFieldName(i, res->field_names());
> +	return (*this)[si];

I rearranged this code so that the most common path is first, and the 
exception is in the 'else' branch.
[patch] BadFieldName exceptionChris Frey9 Feb
  • Re: [patch] BadFieldName exceptionWarren Young14 Feb