a question about g_strconcat()
first, I will show some lines. [code] gchar *str_sample = g_strconcat(I have a, dream that, NULL); str_sample = g_strconcat(str_sample, one day, NULL); str_sample = g_strconcat(str_sample, we can be friends., NULL); // do some work with str_sample g_free(str_sample); [/code] if, for some reasons, I must call g_strconcat() three times, or in concrete, I must follow some conditions to determine whether should I concatenate each of the three phrases okay, actually, I am writing a sql query phrase, like this: if the parameter an_id is a empty string, then I will not append it to the select phrase. select * from a_table where 1=1 and `id`='an_id' and `name`='a_name' actually, I have debug my program and find that each time the str_sample variable has been assigned a different address. But I'm not sure the internal mechanism of g_strconcat(), whether it apply for a totally new space or a space that may overlap with the earlier applied space, if the latter, then I can't free the earlier applied space, and I think it may lead to memory leak. ___ gtk-app-devel-list mailing list gtk-app-devel-list@gnome.org https://mail.gnome.org/mailman/listinfo/gtk-app-devel-list
Re: a question about g_strconcat()
I answered that some time ago: http://stackoverflow.com/questions/11486704/c-sql-query-building-made-easy/11725655#11725655 On Thu, Feb 28, 2013 at 1:22 PM, Cifer Lee mantia...@gmail.com wrote: first, I will show some lines. [code] gchar *str_sample = g_strconcat(I have a, dream that, NULL); str_sample = g_strconcat(str_sample, one day, NULL); str_sample = g_strconcat(str_sample, we can be friends., NULL); // do some work with str_sample g_free(str_sample); [/code] if, for some reasons, I must call g_strconcat() three times, or in concrete, I must follow some conditions to determine whether should I concatenate each of the three phrases okay, actually, I am writing a sql query phrase, like this: if the parameter an_id is a empty string, then I will not append it to the select phrase. select * from a_table where 1=1 and `id`='an_id' and `name`='a_name' actually, I have debug my program and find that each time the str_sample variable has been assigned a different address. But I'm not sure the internal mechanism of g_strconcat(), whether it apply for a totally new space or a space that may overlap with the earlier applied space, if the latter, then I can't free the earlier applied space, and I think it may lead to memory leak. ___ gtk-app-devel-list mailing list gtk-app-devel-list@gnome.org https://mail.gnome.org/mailman/listinfo/gtk-app-devel-list ___ gtk-app-devel-list mailing list gtk-app-devel-list@gnome.org https://mail.gnome.org/mailman/listinfo/gtk-app-devel-list
Re: a question about g_strconcat()
g_strconcat() ALWAYS returns newly allocated memory on each call. Most likely you will have leak when you code like that, because you lost reference. You have to assign it to a new pointer such as: gchar *ptr1 = g_strconcat (ptr1, NULL); gchar *ptr2 = g_strconcat (ptr1, ptr2, NULL); gchar *ptr3 = g_strconcat (ptr2, ptr3, NULL); ... g_free(ptr1); g_free(ptr2); g_free(ptr3); Have a look g_strconcat() function here http://git.gnome.org/browse/glib/tree/glib/gstrfuncs.c#n549 Why not use formatting function such as g_strdup_printf() instead? Also play with GString. ___ gtk-app-devel-list mailing list gtk-app-devel-list@gnome.org https://mail.gnome.org/mailman/listinfo/gtk-app-devel-list
Re: a question about g_strconcat()
thanks very, very much !
I use the mysql database, honestly, I know how to use prepared statement
but earlier, I have learned that too much prepared statement will more or
less increase the burden on the server
was I think too much?
On Thu, Feb 28, 2013 at 8:55 PM, Andrew W. Nosenko
andrew.w.nose...@gmail.com wrote:
On Thu, Feb 28, 2013 at 2:22 PM, Cifer Lee mantia...@gmail.com wrote:
first, I will show some lines.
[code]
gchar *str_sample = g_strconcat(I have a, dream that, NULL);
str_sample = g_strconcat(str_sample, one day, NULL);
Here is memory leak (leak the memory allocated by 1st g_strconcat()).
str_sample = g_strconcat(str_sample, we can be friends., NULL);
And here too (leak the memory allocated by 2nd g_strconcat())
// do some work with str_sample
g_free(str_sample);
[/code]
The simplest way to rewrite your code to not leak and keep similarity
is a use GString.
Your code (g_strconcat() + leak):
{
gchar *str_sample = g_strconcat(I have a, dream that, NULL);
str_sample = g_strconcat(str_sample, one day, NULL);
str_sample = g_strconcat(str_sample, we can be friends., NULL);
// do some work with str_sample
g_free(str_sample);
}
Changed code (GString without leak):
{
GString *str_sample = g_string_new(NULL);
g_string_append(str_sample, I have a);
g_string_append(str_sample, dream that);
g_string_append(str_sample, one day);
g_string_append(str_sample, we can be friends.);
// do some work with str_sample-str
g_string_free(str_sample, TRUE);
}
But see below, please!
if, for some reasons, I must call g_strconcat() three times, or in
concrete, I must follow some conditions to determine whether should I
concatenate each of the three phrases okay, actually, I am writing a
sql query phrase, like this:
if the parameter an_id is a empty string, then I will not append it to
the
select phrase.
select * from a_table where 1=1 and `id`='an_id' and `name`='a_name'
Please! Don't do that! Do not build SQL queries in such way! Step
left, step right -- and you have SQL injection or something even
worse! All more or less sane databases support the prepared
statements and allow to bind variables. I don't know what database
you are using and, therefore, unable give to you the exact names of
function. Please, do not play with fire trying to build the whole SQL
statement with fully and properly quoted and substituted variables!
Use prepared statements instead!
actually, I have debug my program and find that each time the str_sample
variable has been assigned a different address. But I'm not sure the
internal mechanism of g_strconcat(), whether it apply for a totally new
space or a space that may overlap with the earlier applied space, if the
latter, then I can't free the earlier applied space, and I think it may
lead to memory leak.
--
Andrew W. Nosenko andrew.w.nose...@gmail.com
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