He's saying that instead of this:
> fprintf (fp1, r["content"]);
You at least want something like this:
fprintf (fp1, "%s", r["content"]);
if you're going to use fprintf, or, if you want something more
c++-like, you'd use a function besides fprintf altogether.
Otherwise, if your r["content"] happens to return a string that
contains "%s" or some other thing that causes fprintf to look for more
data on the stack, you'll get output you weren't expecting.
--Pete
On Thu, Aug 02, 2007 at 11:04:13AM +0800, wangxu wrote:
> actually I am using this piece of code,but I replaced fprintf to printf
> just to simplify the problem.
> and the field content actually stores string content.
> Shall this mean some thing different from your explanation?
> while (r = res.fetch_row()) {
> FILE *fp1;
> char *fname=new char[50];
> fname[0]='\0';
> strcat(fname,HTML_HOME.c_str());
> strcat(fname,id);
> strcat(fname,".html");
> fp1 = fopen(fname, "w");
> fprintf (fp1, r["content"]);
> fclose(fp1);
> delete fname;
> }
>
> Warren Young wrote:
> >I'm replying to you both personally and to the MySQL++ mailing list,
> >where this message is on topic. Please reply only on the list, not to
> >me directly.
> >
> >wangxu wrote:
> >>below is my code;these code works very fine until, the length of the
> >>field "content" exceeds 300000,
> >
> >How certain are you about this threshold? It seems a very odd number
> >for a computer to care about. If you'd said 65536 bytes, or 16.7 MB,
> >I'd put a lot more credence in your assertion.
> >
> >> mysqlpp::Row r;
> >> while (r = res.fetch_row()) {
> >> printf (r["content"]);
> >> }
> >
> >I'm not sure it's the problem, but you really shouldn't use printf()
> >for this. The main reason is that printf() will scan the resulting
> >string for % signs and try to interpret them as formatting options.
> >If it finds any, it will then try to find varargs, and fail; this
> >would easily explain your segfault. The byte count does affect the
> >chances that this will happen, so maybe that's where your perception
> >that it's data size related comes from.
> >
> >Other reasons not to use printf() with MySQL++ data types are
> >inefficiency and type safety.
> >
> >See examples/cgi_jpeg.cpp for the right way to emit bulk MySQL++ to
> >stdout.
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