If I have an enum
like this:
enum Errors {
ErrorA = 0,
ErrorB,
ErrorC,
};
Then I want to print it out to console:
Errors anError = ErrorA;
std::cout << anError; // 0 wi开发者_JS百科ll be printed
But what I want is the text "ErrorA"
. Can I do it without using if
/switch
? And what is your solution for this?
Using map:
#include <iostream>
#include <map>
#include <string>
enum Errors {ErrorA=0, ErrorB, ErrorC};
std::ostream& operator<<(std::ostream& out, const Errors value){
static std::map<Errors, std::string> strings;
if (strings.size() == 0){
#define INSERT_ELEMENT(p) strings[p] = #p
INSERT_ELEMENT(ErrorA);
INSERT_ELEMENT(ErrorB);
INSERT_ELEMENT(ErrorC);
#undef INSERT_ELEMENT
}
return out << strings[value];
}
int main(int argc, char** argv){
std::cout << ErrorA << std::endl << ErrorB << std::endl << ErrorC << std::endl;
return 0;
}
Using array of structures with linear search:
#include <iostream>
#include <string>
enum Errors {ErrorA=0, ErrorB, ErrorC};
std::ostream& operator<<(std::ostream& out, const Errors value){
#define MAPENTRY(p) {p, #p}
const struct MapEntry{
Errors value;
const char* str;
} entries[] = {
MAPENTRY(ErrorA),
MAPENTRY(ErrorB),
MAPENTRY(ErrorC),
{ErrorA, 0}//doesn't matter what is used instead of ErrorA here...
};
#undef MAPENTRY
const char* s = 0;
for (const MapEntry* i = entries; i->str; i++){
if (i->value == value){
s = i->str;
break;
}
}
return out << s;
}
int main(int argc, char** argv){
std::cout << ErrorA << std::endl << ErrorB << std::endl << ErrorC << std::endl;
return 0;
}
Using switch/case:
#include <iostream>
#include <string>
enum Errors {ErrorA=0, ErrorB, ErrorC};
std::ostream& operator<<(std::ostream& out, const Errors value){
const char* s = 0;
#define PROCESS_VAL(p) case(p): s = #p; break;
switch(value){
PROCESS_VAL(ErrorA);
PROCESS_VAL(ErrorB);
PROCESS_VAL(ErrorC);
}
#undef PROCESS_VAL
return out << s;
}
int main(int argc, char** argv){
std::cout << ErrorA << std::endl << ErrorB << std::endl << ErrorC << std::endl;
return 0;
}
Use an array or vector of strings with matching values:
char *ErrorTypes[] =
{
"errorA",
"errorB",
"errorC"
};
cout << ErrorTypes[anError];
EDIT: The solution above is applicable when the enum is contiguous, i.e. starts from 0 and there are no assigned values. It will work perfectly with the enum in the question.
To further proof it for the case that enum doesn't start from 0, use:
cout << ErrorTypes[anError - ErrorA];
Here is an example based on Boost.Preprocessor:
#include <iostream>
#include <boost/preprocessor/punctuation/comma.hpp>
#include <boost/preprocessor/control/iif.hpp>
#include <boost/preprocessor/comparison/equal.hpp>
#include <boost/preprocessor/stringize.hpp>
#include <boost/preprocessor/seq/for_each.hpp>
#include <boost/preprocessor/seq/size.hpp>
#include <boost/preprocessor/seq/seq.hpp>
#define DEFINE_ENUM(name, values) \
enum name { \
BOOST_PP_SEQ_FOR_EACH(DEFINE_ENUM_VALUE, , values) \
}; \
inline const char* format_##name(name val) { \
switch (val) { \
BOOST_PP_SEQ_FOR_EACH(DEFINE_ENUM_FORMAT, , values) \
default: \
return 0; \
} \
}
#define DEFINE_ENUM_VALUE(r, data, elem) \
BOOST_PP_SEQ_HEAD(elem) \
BOOST_PP_IIF(BOOST_PP_EQUAL(BOOST_PP_SEQ_SIZE(elem), 2), \
= BOOST_PP_SEQ_TAIL(elem), ) \
BOOST_PP_COMMA()
#define DEFINE_ENUM_FORMAT(r, data, elem) \
case BOOST_PP_SEQ_HEAD(elem): \
return BOOST_PP_STRINGIZE(BOOST_PP_SEQ_HEAD(elem));
DEFINE_ENUM(Errors,
((ErrorA)(0))
((ErrorB))
((ErrorC)))
int main() {
std::cout << format_Errors(ErrorB) << std::endl;
}
You can use a simpler pre-processor trick if you are willing to list your enum
entries in an external file.
/* file: errors.def */
/* syntax: ERROR_DEF(name, value) */
ERROR_DEF(ErrorA, 0x1)
ERROR_DEF(ErrorB, 0x2)
ERROR_DEF(ErrorC, 0x4)
Then in a source file, you treat the file like an include file, but you define what you want the ERROR_DEF
to do.
enum Errors {
#define ERROR_DEF(x,y) x = y,
#include "errors.def"
#undef ERROR_DEF
};
static inline std::ostream & operator << (std::ostream &o, Errors e) {
switch (e) {
#define ERROR_DEF(x,y) case y: return o << #x"[" << y << "]";
#include "errors.def"
#undef ERROR_DEF
default: return o << "unknown[" << e << "]";
}
}
If you use some source browsing tool (like cscope), you'll have to let it know about the external file.
This is a good way,
enum Rank { ACE = 1, DEUCE, TREY, FOUR, FIVE, SIX, SEVEN, EIGHT, NINE, TEN, JACK, QUEEN, KING };
Print it with an array of character arrays
const char* rank_txt[] = {"Ace", "Deuce", "Trey", "Four", "Five", "Six", "Seven", "Eight", "Nine", "Ten", "Jack", "Four", "King" } ;
Like this
std::cout << rank_txt[m_rank - 1]
There has been a discussion here which might help: Is there a simple way to convert C++ enum to string?
UPDATE: Here#s a script for Lua which creates an operator<< for each named enum it encounters. This might need some work to make it work for the less simple cases [1]:
function make_enum_printers(s)
for n,body in string.gmatch(s,'enum%s+([%w_]+)%s*(%b{})') do
print('ostream& operator<<(ostream &o,'..n..' n) { switch(n){')
for k in string.gmatch(body,"([%w_]+)[^,]*") do
print(' case '..k..': return o<<"'..k..'";')
end
print(' default: return o<<"(invalid value)"; }}')
end
end
local f=io.open(arg[1],"r")
local s=f:read('*a')
make_enum_printers(s)
Given this input:
enum Errors
{ErrorA=0, ErrorB, ErrorC};
enum Sec {
X=1,Y=X,foo_bar=X+1,Z
};
It produces:
ostream& operator<<(ostream &o,Errors n) { switch(n){
case ErrorA: return o<<"ErrorA";
case ErrorB: return o<<"ErrorB";
case ErrorC: return o<<"ErrorC";
default: return o<<"(invalid value)"; }}
ostream& operator<<(ostream &o,Sec n) { switch(n){
case X: return o<<"X";
case Y: return o<<"Y";
case foo_bar: return o<<"foo_bar";
case Z: return o<<"Z";
default: return o<<"(invalid value)"; }}
So that's probably a start for you.
[1] enums in different or non-namespace scopes, enums with initializer expressions which contain a komma, etc.
I use a string array whenever I define an enum:
Profile.h
#pragma once
struct Profile
{
enum Value
{
Profile1,
Profile2,
};
struct StringValueImplementation
{
const wchar_t* operator[](const Profile::Value profile)
{
switch (profile)
{
case Profile::Profile1: return L"Profile1";
case Profile::Profile2: return L"Profile2";
default: ASSERT(false); return NULL;
}
}
};
static StringValueImplementation StringValue;
};
Profile.cpp
#include "Profile.h"
Profile::StringValueImplementation Profile::StringValue;
This solution doesn't require you to use any data structures or make a different file.
Basically, you define all your enum values in a #define, then use them in the operator <<. Very similar to @jxh's answer.
ideone link for final iteration: http://ideone.com/hQTKQp
Full code:
#include <iostream>
#define ERROR_VALUES ERROR_VALUE(NO_ERROR)\
ERROR_VALUE(FILE_NOT_FOUND)\
ERROR_VALUE(LABEL_UNINITIALISED)
enum class Error
{
#define ERROR_VALUE(NAME) NAME,
ERROR_VALUES
#undef ERROR_VALUE
};
inline std::ostream& operator<<(std::ostream& os, Error err)
{
int errVal = static_cast<int>(err);
switch (err)
{
#define ERROR_VALUE(NAME) case Error::NAME: return os << "[" << errVal << "]" #NAME;
ERROR_VALUES
#undef ERROR_VALUE
default:
// If the error value isn't found (shouldn't happen)
return os << errVal;
}
}
int main() {
std::cout << "Error: " << Error::NO_ERROR << std::endl;
std::cout << "Error: " << Error::FILE_NOT_FOUND << std::endl;
std::cout << "Error: " << Error::LABEL_UNINITIALISED << std::endl;
return 0;
}
Output:
Error: [0]NO_ERROR
Error: [1]FILE_NOT_FOUND
Error: [2]LABEL_UNINITIALISED
A nice thing about doing it this way is that you can also specify your own custom messages for each error if you think you need them:
#include <iostream>
#define ERROR_VALUES ERROR_VALUE(NO_ERROR, "Everything is fine")\
ERROR_VALUE(FILE_NOT_FOUND, "File is not found")\
ERROR_VALUE(LABEL_UNINITIALISED, "A component tried to the label before it was initialised")
enum class Error
{
#define ERROR_VALUE(NAME,DESCR) NAME,
ERROR_VALUES
#undef ERROR_VALUE
};
inline std::ostream& operator<<(std::ostream& os, Error err)
{
int errVal = static_cast<int>(err);
switch (err)
{
#define ERROR_VALUE(NAME,DESCR) case Error::NAME: return os << "[" << errVal << "]" #NAME <<"; " << DESCR;
ERROR_VALUES
#undef ERROR_VALUE
default:
return os << errVal;
}
}
int main() {
std::cout << "Error: " << Error::NO_ERROR << std::endl;
std::cout << "Error: " << Error::FILE_NOT_FOUND << std::endl;
std::cout << "Error: " << Error::LABEL_UNINITIALISED << std::endl;
return 0;
}
Output:
Error: [0]NO_ERROR; Everything is fine
Error: [1]FILE_NOT_FOUND; File is not found
Error: [2]LABEL_UNINITIALISED; A component tried to the label before it was initialised
If you like making your error codes/descriptions very descriptive, you might not want them in production builds. Turning them off so only the value is printed is easy:
inline std::ostream& operator<<(std::ostream& os, Error err)
{
int errVal = static_cast<int>(err);
switch (err)
{
#ifndef PRODUCTION_BUILD // Don't print out names in production builds
#define ERROR_VALUE(NAME,DESCR) case Error::NAME: return os << "[" << errVal << "]" #NAME <<"; " << DESCR;
ERROR_VALUES
#undef ERROR_VALUE
#endif
default:
return os << errVal;
}
}
Output:
Error: 0
Error: 1
Error: 2
If this is the case, finding error number 525 would be a PITA. We can manually specify the numbers in the initial enum like this:
#define ERROR_VALUES ERROR_VALUE(NO_ERROR, 0, "Everything is fine")\
ERROR_VALUE(FILE_NOT_FOUND, 1, "File is not found")\
ERROR_VALUE(LABEL_UNINITIALISED, 2, "A component tried to the label before it was initialised")\
ERROR_VALUE(UKNOWN_ERROR, -1, "Uh oh")
enum class Error
{
#define ERROR_VALUE(NAME,VALUE,DESCR) NAME=VALUE,
ERROR_VALUES
#undef ERROR_VALUE
};
inline std::ostream& operator<<(std::ostream& os, Error err)
{
int errVal = static_cast<int>(err);
switch (err)
{
#ifndef PRODUCTION_BUILD // Don't print out names in production builds
#define ERROR_VALUE(NAME,VALUE,DESCR) case Error::NAME: return os << "[" #VALUE "]" #NAME <<"; " << DESCR;
ERROR_VALUES
#undef ERROR_VALUE
#endif
default:
return os <<errVal;
}
}
ERROR_VALUES
#undef ERROR_VALUE
#endif
default:
{
// If the error value isn't found (shouldn't happen)
return os << static_cast<int>(err);
break;
}
}
}
Output:
Error: [0]NO_ERROR; Everything is fine
Error: [1]FILE_NOT_FOUND; File is not found
Error: [2]LABEL_UNINITIALISED; A component tried to the label before it was initialised
Error: [-1]UKNOWN_ERROR; Uh oh
#include <iostream>
using std::cout;
using std::endl;
enum TEnum
{
EOne,
ETwo,
EThree,
ELast
};
#define VAR_NAME_HELPER(name) #name
#define VAR_NAME(x) VAR_NAME_HELPER(x)
#define CHECK_STATE_STR(x) case(x):return VAR_NAME(x);
const char *State2Str(const TEnum state)
{
switch(state)
{
CHECK_STATE_STR(EOne);
CHECK_STATE_STR(ETwo);
CHECK_STATE_STR(EThree);
CHECK_STATE_STR(ELast);
default:
return "Invalid";
}
}
int main()
{
int myInt=12345;
cout << VAR_NAME(EOne) " " << VAR_NAME(myInt) << endl;
for(int i = -1; i < 5; i)
cout << i << " " << State2Str((TEnum)i) << endl;
return 0;
}
You could use a stl map container....
typedef map<Errors, string> ErrorMap;
ErrorMap m;
m.insert(ErrorMap::value_type(ErrorA, "ErrorA"));
m.insert(ErrorMap::value_type(ErrorB, "ErrorB"));
m.insert(ErrorMap::value_type(ErrorC, "ErrorC"));
Errors error = ErrorA;
cout << m[error] << endl;
For this problem, I do a help function like this:
const char* name(Id id) {
struct Entry {
Id id;
const char* name;
};
static const Entry entries[] = {
{ ErrorA, "ErrorA" },
{ ErrorB, "ErrorB" },
{ 0, 0 }
}
for (int it = 0; it < gui::SiCount; ++it) {
if (entries[it].id == id) {
return entries[it].name;
}
}
return 0;
}
Linear search is usually more efficient than std::map
for small collections like this.
How about this?
enum class ErrorCodes : int{
InvalidInput = 0
};
std::cout << ((int)error == 0 ? "InvalidInput" : "") << std::endl;
etc... I know this is a highly contrived example but I think it has application where applicable and needed and is certainly shorter than writing a script for it.
Use the preprocessor:
#define VISIT_ERROR(FIRST, MIDDLE, LAST) \
FIRST(ErrorA) MIDDLE(ErrorB) /* MIDDLE(ErrorB2) */ LAST(ErrorC)
enum Errors
{
#define ENUMFIRST_ERROR(E) E=0,
#define ENUMMIDDLE_ERROR(E) E,
#define ENUMLAST_ERROR(E) E
VISIT_ERROR(ENUMFIRST_ERROR, ENUMMIDDLE_ERROR, ENUMLAST_ERROR)
// you might undefine the 3 macros defined above
};
std::string toString(Error e)
{
switch(e)
{
#define CASERETURN_ERROR(E) case E: return #E;
VISIT_ERROR(CASERETURN_ERROR, CASERETURN_ERROR, CASERETURN_ERROR)
// you might undefine the above macro.
// note that this will produce compile-time error for synonyms in enum;
// handle those, if you have any, in a distinct macro
default:
throw my_favourite_exception();
}
}
The advantage of this approach is that: - it's still simple to understand, yet - it allows for various visitations (not just string)
If you're willing to drop the first, craft yourself a FOREACH() macro, then #define ERROR_VALUES() (ErrorA, ErrorB, ErrorC)
and write your visitors in terms of FOREACH(). Then try to pass a code review :).
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