Cpp initialize std::map in header

Question

I want to initialize a std::map in my_cpp.h header file:

std::map<std::string, double> my_map;
my_map["name1"] = 0;
my_map["name2"] = 0;

But there was a compile error showed up:

error: ‘my_map’ does not name a type

Can someone explain why this not work for a C++ newbie? Thanks

std::map<std::string, double> my_map{{"name1", 0}, {"name2", 0}}; — Igor Tandetnik
– Igor Tandetnik, Commented Oct 12, 2021 at 3:08
Answering your question: your code doesn't work because statements must be within a body of some function. Only declarations can be present outside any function. — Igor Tandetnik
– Igor Tandetnik, Commented Oct 12, 2021 at 3:10
Thanks all the help above and the below, seems this is a very beginner and stupid question... — Jim Chen
– Jim Chen, Commented Oct 12, 2021 at 6:45

Remy Lebeau · Accepted Answer · 2021-10-12 03:12:39Z

2

You can't initialize a map in a .h file like that. Those assignment statements need to be inside a function/method instead.

Otherwise, initialize the map directly in its declaration, eg

std::map<std::string, double> my_map = {
    {"name1", 0.0},
    {"name2", 0.0}
};

answered Oct 12, 2021 at 3:12

Remy Lebeau

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Comments

alonegame · Accepted Answer · 2021-10-12 03:15:38Z

1

The header file is just a declaration, or initialize the map directly . You can modify your code like this:

#include <map>
#include <string>

const std::map<std::string, double> my_map = {
  { "name1", 0 },
  { "name2", 0 }
};

answered Oct 12, 2021 at 3:15

alonegame

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The other answered first so I have him the as the resolution. But still appreciate for the help.