Error compile Android NDK error: 'strtof' is not a member of 'std'

[fh127]

hi, can you help me, this error occurs when it compile with Android NDK

          error: 'strtof' is not a member of 'std'
         return std::strtof(reinterpret_cast<typename string_t::const_pointer>(m_start), endptr);

         error: 'ERANGE' was not declared in this scope
         if (reinterpret_cast<lexer_char_t*>(endptr) != m_cursor || errno == ERANGE)

[Teemperor]

For ERANGE see the PR. However, the std::strtof in the latest NDK STL looks fine to me and seems to be correctly used in this project. So I would say that there is a problem in your project setup (outdated NDK, weird defines, wrong STL?) and you rather find a solution in an Android developer forum :).

Also try to only run the preprocessor on the problematic source code and check if the included headers are actually defining strtof and are using them in the std namespace (e.g. by running GCC -E ...).

[nlohmann]

I merged PR #222. @fh127, is your issue solved by this?

[vjjjv]

I came across the same problem (in my project, changing or tweaking NDK settings was not an option because of other dependancies) and ended up fixing using a workaround. I hope there would be a cleaner solution though.. What I did:

For GCC 4.9 (for example ndk r10d):

Add to_string in the beginning of json.hpp

#include <vector>

#ifdef JSON_ANDROID_WORKAROUNDS
namespace std
{
    template < typename T > std::string to_string(const T& n)
    {
        std::ostringstream stm;
        stm << n;
        return stm.str();
    }
}
#endif

// disable float-equal warnings on GCC/clang

Use strtod in two places (warning! this will of course lose precision and maybe other errors):

        long double str_to_float_t(long double* /* type */, char** endptr) const
        {
#ifdef JSON_ANDROID_WORKAROUNDS
            return std::strtod(reinterpret_cast<typename string_t::const_pointer>(m_start), endptr);
#else
            return std::strtold(reinterpret_cast<typename string_t::const_pointer>(m_start), endptr);
#endif
        }

        float str_to_float_t(float* /* type */, char** endptr) const
        {
#ifdef JSON_ANDROID_WORKAROUNDS
            return std::strtod(reinterpret_cast<typename string_t::const_pointer>(m_start), endptr);
#else
            return std::strtof(reinterpret_cast<typename string_t::const_pointer>(m_start), endptr);
#endif
        }

For GCC 4.8 this was also needed (ndk r9c):

#ifdef JSON_ANDROID_WORKAROUNDS
    basic_json() {};
#else
    basic_json() = default;
#endif

[fh127]

Hi, @nlohmann , I tested the commit PR #222, when I am compiling in Android NDK, this error was solved:
error: 'ERANGE' was not declared in this scope'''
But I have more errores:
error: 'strtof' is not a member of 'std'
error: 'strtoll' is not a member of 'std'

I am using the Android NDK configuration, and doesn't support those function c. Application.MK:

                APP_STL := gnustl_static
                APP_CPPFLAGS :=  -std=c++11 -frtti -fexceptions
                APP_ABI :=  armeabi armeabi-v7a x86 arm64-v8a
                 NDK_TOOLCHAIN_VERSION := 4.9

this commit of the repository #c0bb5a5 work fine for my Android project

[Dimon4eg]

I use CrystaX NDK and it compiles all fine for android.

[nlohmann]

@fh127 @Dimon4eg As the code works in your cases, could you please give me a detailed version number of your NDK/GCC so that I can mention it in the README file?

@vjjjv I don't want to add these adjustments to my code, because GCC 4.8 is not supported anyway.

[Dimon4eg]

Instead of Google NDK I use CrystaX NDK (latest 10.3.1 from https://www.crystax.net).

[vjjjv]

How about the GCC 4.9, I posted two workarounds for that too?

Its just a bit uncomfortable that a great lib is not compatible with some common dev envs because of such a small changes.. Or am I missing some bigger issues here? Is it so that it's not recommended to use the lib with changes that I made? (I am not super familiar with c++11 "specialities")

[gregmarr]

@vjjjv Can you not use the c++-shared standard library to get the missing to_string function?

[vjjjv]

I am not sure, because I experience this problem using Unity and Qt frameworks for example - there the NDK settings come predefined and its not very clear if I can change them easily.

[nlohmann]

Can someone please provide an example project so I can try to execute the build myself? (I have no experience with Android NDK - I just want to install it in an Ubuntu VM and try it myself.)