如何在Android中使用std :: stoul和std :: stoull？

Question

C++ 11有两个新的字符串转换函数为unsigned long和long long:std::stoul()和std::stoll().

最近的Android NDK r9引入了Clang 3.3编译器,据称它是完整的C++ 11功能.NDK内部有这些函数的原型,但是我不能使用它们.

使用它们需要做什么？

PS我已经做到了LOCAL_CPPFLAGS += -std=c++11

Answer 1

你不能使用这些功能的原因是根深蒂固的,不幸的是目前无法解决.

查看libs/armeabi-v7a/include/bits/c++config.hgnu stdlibc ++文件夹中的文件,您将看到:

...
/* 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 */
...

以上,结合下面的bits/basic_string.h拼写坏消息片段:

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

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

因此,这些功能在NDK中不可用.

根本原因:根本原因似乎是在armeabi-v7a平台上的GNU stdlibc ++中禁用了C99功能使用,因为Bionic libc不支持复杂的数学运算(Android上的标准C库是Bionic) .

可能的修复(未经测试):探索CrystaX的Android NDK,它似乎比Vanilla Android NDK有扩展.

注: __GXX_EXPERIMENTAL_CXX0X__通过添加定义-std=gnu++11到APP_CXXFLAGS或LOCAL_CXXFLAGS

详细测试日志:使用NDK版本r8e
jni/Application.mk构建:

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);
}

Nexus 4(Android 4.3)上的输出:

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.

Answer 2

添加:

APP_STL:= c ++ _ static

到Application.mk解决了我无法访问std :: stoi()的问题(使用gcc 4.8.4).

来自Google网上论坛帖子的 Daniel Tavares解决方案.