Newbie issue: how does one convert a map in Json back to std::map? #600
Comments
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I assume |
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Correct |
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Interestingly, the issue is if the value is a This works: #include "json.hpp"
using json = nlohmann::json;
int main()
{
// create a map
std::map<std::string, int> m1 {{"key", 1}};
// create and print a JSON from the map
json j = m1;
std::cout << j << std::endl;
// get the map out of JSON
std::map<std::string, int> m2 = j;
// make sure the roundtrip succeeds
assert(m1 == m2);
}This does not: #include "json.hpp"
using json = nlohmann::json;
int main()
{
// create a map
std::map<std::string, std::string> m1 {{"key", "val"}};
// create and print a JSON from the map
json j = m1;
std::cout << j << std::endl;
// get the map out of JSON
std::map<std::string, std::string> m2 = j;
// make sure the roundtrip succeeds
assert(m1 == m2);
} |
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Error message: |
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One work around I found is using an iterator feature that was presented in another un-related issue. With an iterator I can get access to each key/value pair. Perhaps this is a good work around until the issue is fully resolved |
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I'm glad it wasn't me being a total newbie. It seemed like I was using valid syntax. |
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Just for reference - how does your solution look like? |
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I'll post it once I get back to my home computer. Unfortunately, my day job does not include compilers anymore. |
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This was my solution: const json& rh = j["rightHand"];
for (auto& element : json::iterator_wrapper(rh)) {
std::cout << element.key() << " maps to " << element.value() << std::endl;
} |
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note that if you take the above and do a std::string(element.value()), the same error occurs as you posted above |
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This is due to the implementation of It's weird that it works with I think we should first convert from all |
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I think this should be tagged as a confirmed bug |
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@theodelrieu Do you see a way to fix this? |
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I will try to fix it this morning, I'll take a look at #607 too |
theodelrieu
added a commit
to theodelrieu/json
that referenced
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Jun 6, 2017
Instead of calling CompatibleObjectType iterator-range constructor, first convert json::value_type to CompatibleObjectType::value_type
nlohmann
added
the
solution: proposed fix
nlohmann
added a commit
that referenced
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Jun 7, 2017
Add pair support, fix CompatibleObject conversions (fixes #600)
nlohmann
removed
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solution: proposed fix
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I think this issue is still solved with #615, there is a test that converts to |
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You are right, this still works. I shall add a regression test and close this issue. |
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Actually, the test is inside |
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No, it's fine to have the tests inside the proper functional suite. But a regression test gives me a better feeling on top of it. |
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Is it possible that there is still an error when using the assignment operator of std::map? |
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Hi I think there is still an issue with certain key/value type combinations. I can't seem to get <int, double> to work. EDIT: Or is this due to the fact that int doesn't convert implicitly to string? |
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@FrotBot What is the compiler error? |
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Looks like something is broken with SFINAE checks. Sigh... I'll fix it on Monday, could you just open a new issue please? Thanks for the report. |
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yes, thank you very much! |
This works for me. |
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I have a map..
But when I go to retrieve the map I get an 'call of overload is ambiguous' type error:
Could you perhaps point me to where I can find an example of how to do this properly? I've searched but can't seem to find anything directly on point
Thanks!
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