C++ File IO in android studio

Question

std::ofstream fout;
fout.open("/sdcard/AudioMixer/output.pcm");
if(!fout.is_open()) {
    __android_log_print(ANDROID_LOG_ERROR,"__main","output file is not opened");
    return -1;
}
fout.close();

i wrote this code on c++ and call function using JNI but fout.is_open() always returns false.