Example C program. gcc test.c; ./a.out; This verifies that strlen on unsigned char array gives the length of content and not the length of array.

test.c

#include <stdio.h>
#include <string.h>

static unsigned char push_cert_sha1[20];

int main() {
	printf("Length = %d", strlen(push_cert_sha1));
	sprintf(push_cert_sha1, "Hello");
	printf("Length = %d", strlen(push_cert_sha1));
}