CODEWITHSUNDEEP
c++dictionaryheader-filestypedef
rbennett485
rbennett485

Reputation: 2163

Error when adding typedef in header

I'm new to C++, and I'm learning from Accelerated C++ (for anyone with the book, I'm trying to run the program described in §7.4)

The program I'm looking at uses some typedefs - I gather that if I add these to a header file, any source file which includes that header will be able to use the typedefs too.

My header is:

#ifndef READ_GRAMMAR_H_INCLUDED
#define READ_GRAMMAR_H_INCLUDED

typedef std::vector<std::string> Rule;
typedef std::vector<Rule> Rule_collection;
typedef std::map<std::string, Rule_collection> Grammar;

Grammar read_grammar(std::istream& in);

#endif // READ_GRAMMAR_H_INCLUDED

This is giving me the error error: 'map' in namespace 'std' does not name a type

If I change the third typedef to typedef std::vector<Rule_collection> Grammar; (not that I want this, just for example) it builds with no errors.

Any idea what the problem is? I have no idea whether I'm doing something trivial the wrong way, or whether the whole approach is incorrect

Upvotes: 1

Views: 670

Answers (2)

ChajusSaib
ChajusSaib

Reputation: 167

You must include the header files, if you don't have them included then how is your program going to use it?

#ifndef READ_GRAMMAR_H_INCLUDED
#define READ_GRAMMAR_H_INCLUDED

#include <istream>
#include <string>
#include <vector>
#include <map>

typedef std::vector<std::string> Rule;
typedef std::vector<Rule> Rule_collection;
typedef std::map<std::string, Rule_collection> Grammar;

Grammar read_grammar(std::istream& in);

#endif // READ_GRAMMAR_H_INCLUDED

Upvotes: 3

rr-
rr-

Reputation: 14831

It says it cannot find map in namespace std. You need to include it so that the compiler can find it. Similarly, you'll need to include headers for std::vector std::string and std::istream:

#ifndef READ_GRAMMAR_H_INCLUDED
#define READ_GRAMMAR_H_INCLUDED
#include <map>
#include <vector>
#include <string>
#include <istream>

typedef std::vector<std::string> Rule;
typedef std::vector<Rule> Rule_collection;
typedef std::map<std::string, Rule_collection> Grammar;

Grammar read_grammar(std::istream& in);

#endif // READ_GRAMMAR_H_INCLUDED

If you feel courageous, you might also want to read about forward declarations - their usage, pros and cons, but I doubt it's needed in this particular case.

Upvotes: 3

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