Unknown type name error when inserting into unordered_map

Question

I have a single file called main.cpp where I am trying to declare an unordered_map as shown below.

std::unordered_map<std::string, std::set<int>> firstSets;

I then try to insert a new (key, value) pair into the map as follows.

std::string decl = "decl";
std::set<int> declFirstSet = {VOID_TOK, INT_TOK, FLOAT_TOK, BOOL_TOK};
firstSets[decl] = declFirstSet;

When I do this I get the following compiler error.

C++ requires a type specifier for all declarations

firstSets[decl] = declFirstSet;

size of array has non-integer type 'std::string' (aka 'basic_string')

firstSets[decl] = declFirstSet;

So it seems to think I am declaring 'firstSets' when I am actually tring to insert into it. And it seems to treat 'firstSets' as an array instead of an unordered_map. How do I fix this?

Are those declarations/expression at global scope (outside of a function)? — 1201ProgramAlarm
– 1201ProgramAlarm, Commented Oct 31, 2021 at 20:23
You can't have expressions in global scope. firstSets[decl] = declFirstSet; needs to be inside a function. You could also initialize it using the constructor when you define it. — 1201ProgramAlarm
– 1201ProgramAlarm, Commented Oct 31, 2021 at 20:29
ok that worked, thanks. Why can't you have expressions at the global scope? — Tom Finet
– Tom Finet, Commented Oct 31, 2021 at 20:33

Bo R · Accepted Answer · 2021-10-31 20:44:00Z

1

Your std::make_pair is wrong. To get closer you need a std::set<int> instead of the std::set.

But what you really want is to just let to compiler make it for you:

    firstSets.insert(std::make_pair(decl, declFirstSet));

or use an easier syntax:

    firstSets[decl] = declFirstSet;

EDIT AFTER UNDERSTANDING THE PROBLEM On the otherhand, you want firstSets to come with initial content you can reorder the declarations:

#include <set>
#include <string>
#include <unordered_map>

std::string decl{"decl"};
std::set<int> declFirstSet{1, 2, 3, 4};
std::unordered_map<std::string, std::set<int>> firstSets{{decl, declFirstSet}};

int main() {}

edited Oct 31, 2021 at 20:44

answered Oct 31, 2021 at 20:07

Bo R

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7 Comments

Tom Finet Over a year ago

I have edited my question to reflect the changes you have suggested. @Bo R

Bo R Over a year ago

My test of you code looke like this

#include <set> #include <string> #include <unordered_map> int main() {     std::unordered_map<std::string, std::set<int>> firstSets;     std::string decl = "decl";     std::set<int> declFirstSet = {1, 2, 3, 4};     firstSets[decl] = declFirstSet; }

Since you're not show all the code the the problem is likely earlier in the source code of macros involing VOID_TOK and the other values, or a missing header. Hard to tell.

Tom Finet Over a year ago

My code is not in a main function, it is at the global scope. I will update to show more detailed code. @Bo R

Bo R Over a year ago

@TomFinet, I know understand the problem. You cannot have an expression in a scope outside of a function. Thus firstSets[decl] = declFirstSet; is being tried as a declaration (which it is not) by the compiler. Having void somefunctionname() { firstSets[decl] = declFirstSet; } is the best you can do.

vmp Over a year ago

The "easier" syntax has different semantics. That might lead to subtle bugs if he thinks they do exactly the same thing...

|

vmp · Accepted Answer · 2021-10-31 20:40:39Z

1

I don't know why it is not working, but you don't need to call make_pair... Changing the insertion line to:

firstSets.insert({decl, declFirstSet});

Should solve your problem.

Here would be a full code example:

#include <set>
#include<string>
#include <unordered_map>
using namespace std;
int main()
{
    std::unordered_map<std::string, std::set<int>> firstSets;
    set<int> s = { 1, 2, 3 };
    firstSets.insert({ "key", s });   
}

But seems like you want them declared in global scope, so you would initialize like the following code:

#include <set>
#include<string>
#include <unordered_map>
using namespace std;

set<int> s1 = { 1, 2, 3 }, s2 = { 4, 5, 6 };
std::unordered_map<std::string, std::set<int>> firstSets{ {"key1", s1}, {"key2", s2}};
int main()
{
}

edited Oct 31, 2021 at 20:40

answered Oct 31, 2021 at 20:05

vmp

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3 Comments

Tom Finet Over a year ago

The error still persists. It still says: "unknown type name 'firstSets' " and "cannot use dot operator on a type". @vmp

Bo R Over a year ago

@vmp, you must include <string> in you example.

vmp Over a year ago

oh, yeah... visual studio seems to add it under the hood, will fix that!

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