C++ enumerate
Mapping enumerate value to a string
In C, normally when you want to map a enumerate value to a string, to print it, we can implement like this.
typedef enum {
none = 0,
pass,
fail
} enVerdictValueType;
const char *VERDICT_STR[] = {
[none] = "NONE",
[pass] = "PASS",
[fail] = "FAIL"
}
void func(enVerdictValueType val)
{
// because of enum type, some time we could push int value to variable "val"
// incase of val receive from other source, it could cause out of array access if we don't check it carefully
printf("VERDICT: %s\r\n", VERDICT_STR[val]);
}Let try to improve above print enum implementation in C++.
#include <vector>
// create a general class that will do the enumerate mapping with string and do the checking
class EnumMap
{
private:
// vector to store the const string for enum map
std::vector<const char*> table;
// string to print when input enum value is out of index range
const char* ERROR_STRING = "OUT_OF_RANGE";
public:
// && is rvalue reference, specify rvalue because we initialize
// the string vector table with rvalue
EnumMap(std::vector<const char*>&& input_table)
: table(std::move(input_table)) {}
~EnumMap() {}
// override the operator []
const char* operator[](ssize_t idx) const
{
// index checking
if ((idx < 0) || ((size_t)idx > table.size()))
{
// return ERROR string incase of input value is not exist in enum type
return ERROR_STRING;
}
else
{
// return corresponding string
return table[idx];
}
}
};
// here is the part we using
// create enum
typedef enum {
none = 0,
pass,
fail
} enVerdictValueType;
// create corresponding enum string map with easier syntax
const EnumMap VERDICT_STR({"NONE", "PASS", "FAIL"});
// use it
>> std::cout << VERDICT_STR[pass] << std::endl;How about when you have a enumerate with its value does not span continuously, We could modify the EnumMap to use std::unordered_map<int, std::string> instead of std::vector
#include <unordered_map>
typedef enum {
none = 0,
pass = 22, // << weird, but could happen
fail = 12
} enVerdictValueType;
const EnumMap VERDICT_STR({
{none, "NONE"}, // << have to provide the index corresponding with string
{pass, "PASS"},
{fail, "FAIL"}});
class EnumMap
{
private:
// unordered_map to store the const string for enum map
std::unordered_map<int, const char*> table;
// string to print when input enum value is not existed
const char* ERROR_STRING = "OUT_OF_RANGE";
public:
// && is rvalue reference, specify rvalue because we initialize
// the string vector table with rvalue
EnumMap(std::unordered_map<int, const char*>&& input_table)
: table(std::move(input_table)) {}
~EnumMap() {}
// override the operator []
const char* operator[](ssize_t idx) const
{
// index checking
if (0 == table.count(idx))
{
// return ERROR string incase of input value is not exist in enum type
return ERROR_STRING;
}
else
{
// return corresponding string
return table.at(idx);
}
}
};Above class implementation help us initialize enumerate string map easier and less error-prone.