C++ Multidimensional string array initialization (std::map)

Question

I have this special array of strings in c++:

#include <map>
#include <string>

std::map<std::string, std::map<int, std::string>> oParam;
oParam["pA"][0] = "a";
oParam["pA"][1] = "b";
oParam["pA"][2] = "c";
oParam["pB"][0] = "x";
oParam["pB"][1] = "y";
oParam["pB"][2] = "z";

But I would like to initialize it with an initialization list, something like this:

std::map<std::string, std::map<int, std::string>> oParam{
    { "pA", { "a", "b", "c" } },
    { "pB", { "x", "y", "z" } },
};

But this is giving me an error. Am I missing some brackets?

Jerry Coffin · Accepted Answer · 2015-05-13 22:56:36Z

3

If the integers acting as keys in the internal map are going to be contiguous, you could just use a vector instead:

std::map<std::string, std::vector<std::string>> oParam;

With that, the initialization you've given should work.

If you continue to use a std::map instead, you'll have to do a couple of things. First, it supports sparse keys, so you'll need to specify the key for each string you want to insert. Second, you'll need to enclose all the items to insert into one map in braces, something like this:

std::map<std::string, std::map<int, std::string>> oParam {
    { "pA", { { 0, "a" }, { 1, "b" }, { 2, "c" } } },
    { "pB", { { 0, "x" }, { 1, "y" }, { 2, "z" } } }
};

edited May 13, 2015 at 22:56

answered May 13, 2015 at 22:45

Jerry Coffin

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1 Comment

Ilyssis Over a year ago

Thx for the vector solution!

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