error: implicit declaration of function 'posix_memalign' [-Werror=implicit-function-declaration]

采用NDK版本Android-21编译的文件在android-21以下版本(4.4.2)可能出现以下问题：

error: undefined reference to 'atof'

参考:https://code.google.com/p/android/issues/detail?id=77861

When i use NDK r10b build success

APP_ABI := armeabi-v7a-hard

APP_PLATFORM := android-19

but when use NDK r10c, platform targe android-21, compile ok, but run error: dlopen failed: cannot locate symbol "atof" referenced

APP_ABI := armeabi-v7a-hard
APP_PLATFORM := android-21

解决办法：

下载并修改NDK中API 17,18,19中的libstd.h文件

下载地址：unzip -v posix_memalign_decl_17_18_19.zip

Ubuntu下操作方法：

unzip -v posix_memalign_decl_17_18_19.zip

Archive:  posix_memalign_decl_17_18_19.zip
Length   Method    Size  Cmpr    Date    Time   CRC-32   Name
--------  ------  ------- ---- ---------- ----- --------  ----
5420  Defl:N     1993  63% 2014-10-22 10:38 85fa17d2  platforms/android-17/arch-arm/usr/include/stdlib.h
5420  Defl:N     1993  63% 2014-10-22 10:38 85fa17d2  platforms/android-17/arch-mips/usr/include/stdlib.h
5420  Defl:N     1993  63% 2014-10-22 10:38 85fa17d2  platforms/android-17/arch-x86/usr/include/stdlib.h
5420  Defl:N     1993  63% 2014-10-22 10:38 85fa17d2  platforms/android-18/arch-arm/usr/include/stdlib.h
5420  Defl:N     1993  63% 2014-10-22 10:38 85fa17d2  platforms/android-18/arch-mips/usr/include/stdlib.h
5420  Defl:N     1993  63% 2014-10-22 10:38 85fa17d2  platforms/android-18/arch-x86/usr/include/stdlib.h
5420  Defl:N     1993  63% 2014-10-22 10:38 85fa17d2  platforms/android-19/arch-arm/usr/include/stdlib.h
5420  Defl:N     1993  63% 2014-10-22 10:38 85fa17d2  platforms/android-19/arch-mips/usr/include/stdlib.h
5420  Defl:N     1993  63% 2014-10-22 10:38 85fa17d2  platforms/android-19/arch-x86/usr/include/stdlib.h
--------          -------  ---                            -------
48780            17937  63%                            9 files

此外，还可以在platform/android-19/arch-arm/usr/include下将stdlib.h文件添加

<span style="font-size:18px;">extern int posix_memalign(void **memptr, size_t alignment, size_t size);</span>