How to access keys of maps using a string pointer

manpreet Best Answer 2 years ago

I am trying to access a map by using a string* pom.tuteehub.com/tag/int">inter instead of its actual value. Whenever I use this pom.tuteehub.com/tag/int">inter the maps key is returning the wrong value.

mymap_comp_for_c.insert(pair<string, unsigned short m.tuteehub.com/tag/int">int>("M", 0b1110000));

_c_parts[1] holds the value of M

but value+= mymap_comp_for_c[c_parts[1]] is returning the incorrect integer that is assigned to "M"

manpreet 2 years ago

A pointer like "M" will not match later another pointer "M" or a &string("M"). It's the same type (const char*) but a different value, and you use as a key the value of the pointer which is different.

map<string*,int> x;
x["m"] = 5;
int y = x["m"]; // y not necessarily 5.  

"m" in line 3 and "m" in the previous line have different pointer values. The compiler might optimize with string pooling, leading you to believe that it worked, but it is actually a hard to find bug.