C語言八大難點揭秘：學(xué)不好編程全賴他們

void?f1(char?*explanation)
{
??char?p1;
??p1?=?malloc(100);
??sprintf(p1,"The?f1?error?occurred?because?of?'%s'.",explanation);
??local_log(p1);
}

int?getkey(char?*filename)
{
????FILE?*fp;
????int?key;
????fp?=?fopen(filename,?"r");
????fscanf(fp,?"%d",?&key);
????return?key;
}

void?f2(int?datum)
{
???int?*p2;
???/*?Uh-oh!??No?one?has?initialized?p2.?*/
???*p2?=?datum;
???...
}

/*?Allocate?once,?free?twice.?*/
void?f3()
{
????char?*p;
????p?=?malloc(10);
?????...
????free(p);
?????...
????free(p);
}

/*?Allocate?zero?times,?free?once.?*/
void?f4()
{
???char?*p;
???/*?Note?that?p?remains?uninitialized?here.?*/
???free(p);
}

void?f8()
{
???struct?x?*xp;
???xp?=?(struct?x?*)?malloc(sizeof?(struct?x));
???xp.q?=?13;
???...
???free(xp);
???...
/*?Problem!??There's?no?guarantee?that
??the?memory?block?to?which?xp?points
??hasn't?been?overwritten.?*/
??return?xp.q;
}

/********
*?...
*
*?Note?that?any?function?invoking?protected_file_read()
*?assumes?responsibility?eventually?to?fclose()?its
*?return?value,?UNLESS?that?value?is?NULL.
*
********/
FILE?*protected_file_read(char?*filename)
{
????FILE?*fp;

????fp?=?fopen(filename,?"r");
????if?(fp)?{
...
????}?else?{
...
????}
????return?fp;
}

????????/*******
*?...
*
*?Note?that?the?return?value?of?get_message?points?to?a
*?fixed?memory?location.??Do?NOT?free()?it;?remember?to
*?make?a?copy?if?it?must?be?retained?...
*
********/
char?*get_message()
{
????static?char?this_buffer[400];

????????????...
????(void)?sprintf(this_buffer,?...);
????return?this_buffer;
????????}


????????/********
*?...
*?While?this?function?uses?heap?memory,?and?so?
*?temporarily?might?expand?the?over-all?memory
*?footprint,?it?properly?cleans?up?after?itself.
*?
********/
????????int?f6(char?*item1)
{
????my_class?c1;
????int?result;
????????????...
????c1?=?new?my_class(item1);
????...
????????????result?=?c1.x;
????delete?c1;
????return?result;
}
/********
*?...
*?Note?that?f8()?is?documented?to?return?a?value
*?which?needs?to?be?returned?to?heap;?as?f7?thinly
*?wraps?f8,?any?code?which?invokes?f7()?must?be
*?careful?to?free()?the?return?value.
*
********/
int?*f7()
{
????int?*p;

????p?=?f8(...);
????...
????return?p;
}

static?char?*important_pointer?=?NULL;
void?f9()
{
if?(!important_pointer)?
important_pointer?=?malloc(IMPORTANT_SIZE);
????????????...
if?(condition)
/*?Ooops!??We?just?lost?the?reference?important_pointer?already?held.?*/
important_pointer?=?malloc(DIFFERENT_SIZE);
????????????...
}

int?main()
{
char?p[5];
strcpy(p,?"Hello,?world.");
puts(p);
}