A program that writes code: should it use 'string'?

**Kai-Uwe Bux** · Jun 1 '08, 10:15 PM

Re: A program that writes code: should it use 'string'?

Ramon F Herrera wrote:

>
I am writing a program that generates source code. See a snippet
below. My question is about the use of that growing 'code' variable.
Is it efficient? Is is recommended for this case?

Recommended is to measure before you optimize. Write the program so that it
is easy to understand. When (and only when) you have a performance problem,
don't guess what the cause might be; instead, use a profiler to identify
the bottleneck and then do something about it.

The code generated can grow a lot. Perhaps I should allocate a large
max size in advance?

[snip]

If profiling shows that appending to the string is too costly, reserving a
certain capacity would be the first thing to try. It's the least intrusive
measure.

Best

Kai-Uwe Bux

**Daniel T.** · Jun 1 '08, 10:35 PM

Re: A program that writes code: should it use 'string'?

Ramon F Herrera <ramon@conexus. netwrote:

I am writing a program that generates source code. See a snippet
below. My question is about the use of that growing 'code' variable.
Is it efficient? Is is recommended for this case?
>
The code generated can grow a lot. Perhaps I should allocate a large
max size in advance?

A std::string is just a vector<charwith some extra functions that you
probably don't need for this particular variable.

I think your best bet would be to make your own class to represent
"code", implement that class with a string if that makes sense to you.
The nice thing is you can always change the implementation of the class
later as profiling requires, without affecting any other code.

**James Kanze** · Jun 2 '08, 08:35 AM

Re: A program that writes code: should it use 'string'?

On Jun 1, 11:58 pm, Ramon F Herrera <ra...@conexus. netwrote:

I am writing a program that generates source code. See a snippet
below. My question is about the use of that growing 'code' variable.
Is it efficient? Is is recommended for this case?

The code generated can grow a lot. Perhaps I should allocate a large
max size in advance?

-------------

void SynthesizeTextF ield(CompleteFi eld fullTextField)
{
string code;
string baseFieldname = "text";
stringstream ss;
static int subindex = 1;
>
code = "Field ";
code += baseFieldname;
ss << subindex;
code += ss.str();
code += " ";
code += "doc.FieldCreat e(\"";
code += baseFieldname;
code += ss.str();
code += "\", Field::e_text, \"\", \"\");";
>
subindex++;
}

For starters, I'd generate (or support generation) directly into
the output stream. Something like:

std::ostream&
SynthesizeTextF ield(
std::ostream& dest,
... )
{
// ...
return dest ;
}

You're formatting here (some of the data is numeric,
apparently), so you might as well treat the entire thing as a
stream. And you'll certainly be outputting it in the end;
there's not much you can do with C++ source code within the
program, so you might as well generate directly into the output
stream, and never build the string at all.

--
James Kanze (GABI Software) email:james.kan ze@gmail.com
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**Juha Nieminen** · Jun 2 '08, 09:15 AM

Re: A program that writes code: should it use 'string'?

Ramon F Herrera wrote:

I am writing a program that generates source code. See a snippet
below. My question is about the use of that growing 'code' variable.
Is it efficient? Is is recommended for this case?

I think it's ok. You could also say something like
"code.reserve(1 00*1024);" which allocates 100kB (or any other
amount you feel is about correct) of memory for it so that it
never has to resize (unless you exceed that limit, of course),
which might make it slightly more efficient.

A program that writes code: should it use 'string'?

A program that writes code: should it use 'string'?

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