sprintf not working when format contains non-ASCII characters - c++

Question

The following call to sprintf fails when compiled for i386 arch. using the Android NDK. I have tried compiling with both GCC and clang, and the result is the same. I'm using android-ndk-r10e (with APP_STL set to gnustl_shared with GCC, c++_shared with clang). It works as (I?) intended when compiling for ARM with the same configuration, and furthermore when I'm compiling for i386 Linux with GCC 5.2.
int n = sprintf(buf, "\xc0%s", "test"); // n == 0, strlen(buf) == 0
After the call, buf is empty rather than containing the expected char sequence "\xc0test". sprintf appears to ignore everything after the first non-ASCII character. The following code writes "test" to buf, leaving out the last byte:
sprintf(buf, "%s\xc0", "test"); // strlen(buf) == 4
On the other hand, this works fine:
sprintf(buf, "%s", "test\xc0"); // strlen(buf) == 5
I'm perplexed.

Answer 1

This is known Android problem. The problem resides in Android libc implementation (Bionic), which is fairly incomplete in terms of conforming to standards. In particular, Bionic stdio implementation doesn't support non-ASCII characters properly.
This simple test prints strlen(buf)=4 when being built by Android NDK r10e:
#include <stdio.h>
#include <string.h>
int main()
{
char buf[256];
sprintf(buf, "%s\xc0", "test");
printf("strlen(buf)=%d\n", strlen(buf));
return 0;
}
Solution: use CrystaX NDK - alternative fork of the Google's Android NDK, where that problems were fixed. The example above works properly if being built by the CrystaX NDK 10.3.1:
strlen(buf)=5