Re: querry related to STL map..

From:

Thomas Maeder <maeder@glue.ch>

Newsgroups:

comp.lang.c++.moderated

Date:

27 Sep 2006 13:58:05 -0400

Message-ID:

<m2slid6zpq.fsf@glue.ch>

{ extraneous linebreaks removed. -mod }

"ravips" <ravips123@gmail.com> writes:

I have a map<char *,int> it does not work consistently. I have used
similar sort of implementation as below:

map<char *,int> m1;
map<char *,int>::iterator i;

m1["January"] = 31;

Side note: The type of "January" is 'array of 8 char const'. The
implicit conversion of a string literal to 'pointer to char'
(non-const!) that this code relies on is deprecated. Better make the
key type of your map char const *.

m1["February"] = 28;
m1["March"] = 31;
m1["April"] = 30;
m1["May"] = 31;
m1["June"] = 30;
m1["July"] = 31;

This is similar to the map that i have used. Now accessing this yields
different results as below:

Option1:

char *p = "May";
int it = m1[p]; // Works properly returns 31.

Option2:
char *p = new char[3];
strcpy(p, "May");

This copies 4 char objects to an array that can only hold 3 char
objects. Your program has undefined behavior.

int it = m1[p]; // returns 0 .. instead of 31 ....

That's one instance of undefined behavior.

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