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char * to enum

Started by siliconsurfer Sep 16, 2005 at 5:49 AM 6 replies 4.3k views

Original Post

Sep 16, 2005 at 5:49 AM

Hi, quick question. I have a enum type called stage. So I can have write:- stage theStage = first; stage theStage = second; etc etc I was wondering is there any way, if I read in the string "first" from a text file and store it in char *stageString, can I somehow convert the char * to the enum type. i.e stage theStage = stageString; Cheers

ZQJ

Sep 16, 2005 at 6:02 AM

I'm pretty sure the answer is no. You'll have to compare the string against each possibility and assign it yourself.

Sharlin

Sep 16, 2005 at 6:05 AM

Well, no need to compare against all of them, just do a binary search (O(lg n)) or a hash lookup (O(1) average case) in an array of (string, enum) mappings. The easiest way is probably to go with std::map.

Enigma

188

Enigma

Sep 16, 2005 at 6:17 AM

C++:

enum MyEnum{	EnumValue1 = value1,	EnumValue2 = value2};typedef std::map< std::string, MyEnum > StringToEnumTable;typedef StringToEnumTable::const_iterator StringToEnumLookup;StringToEnumTable buildStringToEnumTable(){	StringToEnumTable table;	table.insert(std::make_pair("EnumValue1", EnumValue1));	table.insert(std::make_pair("EnumValue2", EnumValue2));	return table;}StringToEnumTable stringToEnum = buildStringToEnumTable();void someFunction(){	std::ifstream reader("myDataFile.dat");	std::string enumName;	reader >> enumName;	StringToEnumLookup enumValue = stringToEnum.find(enumName);	if (enumValue != stringToEnum.end())	{		doSomething(enumValue->second);	}	else	{		throw EnumValueNotFound(enumName);	}}

moeron seems to have deleted his post while I was replying

Quote:
Original post by moeron
if( !stricmp(szStageOne, currentToken.c_str() ) )

There is a special circle of hell reserved for those who needlessly use C string functions in C++.

Enigma

Kippesoep

Sep 16, 2005 at 7:48 AM

Quote:
Original post by Enigma
Quote:
Original post by moeron
if( !stricmp(szStageOne, currentToken.c_str() ) )
There is a special circle of hell reserved for those who needlessly use C string functions in C++.

If only C++ strings actually contained an easy method to actually do this (that is: case-insensitive comparison). It's not quite as needless as it may seem.

moeron

Sep 16, 2005 at 8:06 AM

Quote:
Original post by Enigma
C++:
*** Source Snippet Removed ***

moeron seems to have deleted his post while I was replying
Quote:
Original post by moeron
if( !stricmp(szStageOne, currentToken.c_str() ) )
There is a special circle of hell reserved for those who needlessly use C string functions in C++.

Enigma

Yeah, I just woke up when I responded. After I read the other poster's map response I realized that may method wasn't of much help

moe.ron

[EDIT]
But even using the map method there are C-String comparisons done on the std::string if you use them as a key-type...

Puzzler183

Sep 16, 2005 at 9:14 AM

Quote:
Original post by Sharlin
Well, no need to compare against all of them, just do a binary search (O(lg n)) or a hash lookup (O(1) average case) in an array of (string, enum) mappings. The easiest way is probably to go with std::map.

O(1) if you ignore the cost of hashing.

flangazor

106

flangazor

Sep 16, 2005 at 12:17 PM

Quote:
Original post by Puzzler183
Quote:
Original post by Sharlin
Well, no need to compare against all of them, just do a binary search (O(lg n)) or a hash lookup (O(1) average case) in an array of (string, enum) mappings. The easiest way is probably to go with std::map.

O(1) if you ignore the cost of hashing.

That's what the O in O(1) is.

I've had the same problem intent as the OP before and used Enigma's solution. However, I make a const array of pairs and build the map with iterators.

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