How to set standard c99 for compile android NDK project - android-ndk

Question

I want to build small library which was written in C99 for Android, but compiler gave log as
note: use option -std=c99 or -std=gnu99 to compile your code
Where can I set it?

Answer 1

In your Android.mk add
LOCAL_CFLAGS += -std=c99
For example:
LOCAL_PATH := $(call my-dir)
include $(CLEAR_VARS)
LOCAL_CFLAGS += -std=c99
LOCAL_SRC_FILES := com_example_ndktest_TestLib.c
LOCAL_MODULE := com_example_ndktest_TestLib
include $(BUILD_SHARED_LIBRARY)
Make sure you add 'LOCAL_CFLAGS' after adding 'include $(CLEAR_VARS)'

Answer 2

An addendum to auselen's answer:
According to the NDK docs (kandroid.org mirror), LOCAL_CFLAGS will only apply to each module - if you want this behavior across an entire project, set APP_CFLAGS in Application.mk. Also, CFLAGS will cover C and C++ sources, CPPFLAGS covers C++ only.

Answer 3

As people may be arriving here looking to "set standard c99 for compile android NDK project", I think this needs an update.
For Android Studio 1.4 with Gradle 2.5, the c99 can be set in build.gradle
NOTE THAT THE CASE SENSITIVE SYNTAX WITHIN BUILD.GRADLE HAS CHANGED FROM cFlags TO CFlags (many examples online use the old syntax).
here is a build.gradle modified from the sample hello-jni project with C99 support added.
apply plugin: 'com.android.model.application'
model {
android {
compileSdkVersion = 23
buildToolsVersion = "23.0.0"
defaultConfig.with {
applicationId = "com.example.hellojni"
minSdkVersion.apiLevel = 4
targetSdkVersion.apiLevel = 23
}
}
compileOptions.with {
sourceCompatibility=JavaVersion.VERSION_1_7
targetCompatibility=JavaVersion.VERSION_1_7
}
/*
* native build settings
*/
android.ndk {
moduleName = "hello-jni"
CFlags += "-std=c99"
}
android.buildTypes {
release {
minifyEnabled = false
proguardFiles += file('proguard-rules.txt')
}
}
android.productFlavors {
// for detailed abiFilter descriptions, refer to "Supported ABIs" #
// https://developer.android.com/ndk/guides/abis.html#sa
create("arm") {
ndk.abiFilters += "armeabi"
}
create("arm7") {
ndk.abiFilters += "armeabi-v7a"
}
create("arm8") {
ndk.abiFilters += "arm64-v8a"
}
create("x86") {
ndk.abiFilters += "x86"
}
create("x86-64") {
ndk.abiFilters += "x86_64"
}
create("mips") {
ndk.abiFilters += "mips"
}
create("mips-64") {
ndk.abiFilters += "mips64"
}
// To include all cpu architectures, leaves abiFilters empty
create("all")
}
}