22

C++11 has two new string conversion functions into unsigned long and long long: std::stoul() and std::stoll().

The recent Android NDK r9 introduces Clang 3.3 compiler which is said to be C++11 feature complete. There are prototypes for these functions deep inside NDK, however I cannot use them.

What do I need to do to use them?

P.S. I already do LOCAL_CPPFLAGS += -std=c++11

Sergey K.
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    Probably similar to this http://stackoverflow.com/questions/15616254/enable-c11-support-on-android. but instead use clangs c++11 library. (I think its `-stdlib=libc++ -std=c++11` for the LOCAL_CFLAGS) – FDinoff Jul 30 '13 at 15:24
  • I already do ``-std=c++11`` – Sergey K. Jul 30 '13 at 16:01
  • `-stdlib=libc++` is also needed make sure you try it – aaronman Jul 30 '13 at 17:14
  • Added -stdlib=libc++ and defined __GXX_EXPERIMENTAL_CXX0X__ Still no success. – Sergey K. Jul 30 '13 at 18:36
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    I have no idea. I can't get this to work. I think some define is missing but I can't tell which. If you do a `-E` to show the preprocessor output you can see that `bits/basic_string.h` is included and that appears to be where `stoll` is defined however `stoll` does not appear in the preprocessor output. – FDinoff Jul 30 '13 at 18:50

2 Answers2

38

The reason why you cannot use the functions is quite deep rooted, and unfortunately currently unsolvable.

Looking into the libs/armeabi-v7a/include/bits/c++config.h file in the gnu stdlibc++ folder, you'll see this:

...
/* Define if C99 functions or macros from <wchar.h>, <math.h>, <complex.h>,
   <stdio.h>, and <stdlib.h> can be used or exposed. */
/* #undef _GLIBCXX_USE_C99 */
...

The above, in conjunction with the following snippet from bits/basic_string.h spells bad news:

...
#if (defined(__GXX_EXPERIMENTAL_CXX0X__) && defined(_GLIBCXX_USE_C99) \
     && !defined(_GLIBCXX_HAVE_BROKEN_VSWPRINTF))

/* The definitions of Numeric Conversions [string.conversions] */
#endif
...

Thus, these functions are unusable in the NDK.

Root Cause: The root cause seems to be that the C99 functionality usage has been disabled in the GNU stdlibc++ on the armeabi-v7a platform due to the fact the the Bionic libc does not support complex math (the standard C library on Android is Bionic).

Possible Fix (untested): Explore CrystaX's Android NDK which seems to have extensions over the Vanilla Android NDK.

Note: __GXX_EXPERIMENTAL_CXX0X__ is defined by adding -std=gnu++11 to APP_CXXFLAGS or LOCAL_CXXFLAGS

Detailed Test log: Built using NDK version r8e
jni/Application.mk:

APP_STL := gnustl_static
APP_CXXFLAGS += -std=gnu++11
NDK_TOOLCHAIN_VERSION := 4.7

jni/Android.mk

LOCAL_PATH := $(call my-dir)
include $(CLEAR_VARS)
LOCAL_MODULE    := cxx11
LOCAL_SRC_FILES := cxx11.cpp
include $(BUILD_EXECUTABLE)

jni/cxx11.cpp:

#include <iostream>
#include <string>

int main(int argc, char* argv[]) {
#if defined(__GXX_EXPERIMENTAL_CXX0X__)
    std::cout<<"__GXX_EXPERIMENTAL_CXX0X__ defined."<<std::endl;
#else
    std::cout<<"__GXX_EXPERIMENTAL_CXX0X__ not defined."<<std::endl;
#endif

#if defined(_GLIBCXX_USE_C99)
    std::cout<<"_GLIBCXX_USE_C99 defined."<<std::endl;
#else
    std::cout<<"_GLIBCXX_USE_C99 not defined."<<std::endl;
#endif

#if defined(_GLIBCXX_HAVE_BROKEN_VSWPRINTF)
    std::cout<<"_GLIBCXX_HAVE_BROKEN_VSWPRINTF defined."<<std::endl;
#else
    std::cout<<"_GLIBCXX_HAVE_BROKEN_VSWPRINTF not defined."<<std::endl;
#endif

#if (defined(__GXX_EXPERIMENTAL_CXX0X__) && defined(_GLIBCXX_USE_C99) \
     && !defined(_GLIBCXX_HAVE_BROKEN_VSWPRINTF))
    std::string s="1";
    std::cout<<"ll:"<<std::stoll(s)<<std::endl<<"ul:"<<std::stoul(s)<<std::endl;
#else
    std::cout<<"No support for stoll/stoul."<<std::endl;
#endif
    return(0);
}

Output on Nexus 4 (Android 4.3):

u0_a51@mako:/ $ /data/local/tmp/cxx11
__GXX_EXPERIMENTAL_CXX0X__ defined.
_GLIBCXX_USE_C99 not defined.
_GLIBCXX_HAVE_BROKEN_VSWPRINTF not defined.
No support for stoll/stoul.
Samveen
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  • Any chance to replace stdlib? – Sergey K. Aug 08 '13 at 11:19
  • @SergeyK. Try [CrystaX's Android NDK](http://www.crystax.net/android/ndk.php), which seems to have some fixes over the Vanilla Android NDK. I am looking to explore it as well. – Samveen Aug 08 '13 at 11:43
  • Have you tried NDK r9? Maybe we can define _GLIBCXX_USE_C99 manually? – Sergey K. Aug 08 '13 at 11:44
  • @SergeyK. Naah. Already tried `LOCAL_CFLAGS := -D _GLIBCXX_USE_C99=1`. It's a very deep-rooted problem. – Samveen Aug 08 '13 at 11:46
  • Ok, this seems to be a great answer. – Sergey K. Aug 08 '13 at 12:17
  • @Leco As I mentioned "Possible fix" section in the answer and in the comment to SergeyK, take a look at [CrystaX's Android NDK](https://www.crystax.net/android/ndk.php), which is a rebuild of the standard NDK with full C++11 support – Samveen Dec 06 '14 at 15:43
  • Thanks. I only needed std:stol so I copied the implementation from source and used it in my project. – Luis Dec 06 '14 at 17:24
  • For anyone landing here years later, the current fix is to switch to libc++ (`APP_STL := c++_shared` if you're using ndk-build). It doesn't have these problems. – Dan Albert Jul 30 '18 at 21:55
  • @DanAlbert please post a solution instead of this comment. Better for all that way. – Samveen Aug 02 '18 at 10:23
  • @DanAlbert the question is about `std::stoul` while the answer by Mark S. is about `std::stoi`. – Samveen Aug 10 '18 at 05:12
  • It's the same problem. – Dan Albert Aug 22 '18 at 22:20
7

Adding:

APP_STL := c++_static

to Application.mk fixed my issue of not being able to access std::stoi() (using gcc 4.8.4).

solution via Daniel Tavares, from this Google Groups post.

Mark S.
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