Testing BeOS R5 MemoryIO behavior for https://review.haiku-os.org/c/haiku/+/2066

output.txt

$ uname -a
BeOS trantor 5.0 1000009 BePC unknown
$ g++ test.cpp -o test -lbe
$ ./test
Running test 1
Running test 2
Running test 3
Running test 4
ERROR: 5 != -2147483643
ERROR: 1111556103 != 7
Running test 5   

test.cpp

#include <iostream>
#include <string.h>

#include <DataIO.h>

template <typename A, typename B>
void assert_equal(const A& a, const B& b) {
  if (a != b) {
  	std::cerr << "ERROR: " << a << " != " << b << std::endl;
  }
}

int main()
{
	char buf[10];
	const char *writeBuf = "ABCDEF";
	
	BMemoryIO mem(buf, 10);
	ssize_t err;
	off_t pos;

	std::cout << "Running test 1" << std::endl;	
	memset(buf, 0, 10);
	pos = mem.Position();
	err = mem.Write(writeBuf, 7);
	assert_equal(err, 7);
	assert_equal(strcmp(writeBuf, buf), 0);
	assert_equal(mem.Position(), pos + err);

	std::cout << "Running test 2" << std::endl;
	memset(buf, 0, 10);
	pos = mem.Position();
	err = mem.WriteAt(3, writeBuf, 2);
	assert_equal(err, 2);
	assert_equal(strncmp(buf + 3, writeBuf, 2), 0);
	assert_equal(mem.Position(), pos);
	
	std::cout << "Running test 3" << std::endl;
	memset(buf, 0, 10);
	pos = mem.Position();
	err = mem.WriteAt(9, writeBuf, 5);
	assert_equal(err, 1);
	assert_equal(strncmp(buf + 9, writeBuf, 1), 0);
	assert_equal(mem.Position(), pos);
	
	std::cout << "Running test 4" << std::endl;
	memset(buf, 0, 10);
	pos = mem.Position();
	err = mem.WriteAt(-10, writeBuf, 5);
	assert_equal(err, B_BAD_VALUE);
	assert_equal(mem.Position(), pos);

	std::cout << "Running test 5" << std::endl;
	memset(buf, 0, 10);
	BMemoryIO read_only_mem(const_cast<const char*>(buf), 10);
	pos = read_only_mem.Position();
	err = read_only_mem.WriteAt(3, writeBuf, 2);
	assert_equal(err, B_NOT_ALLOWED);
	assert_equal(read_only_mem.Position(), pos);
	
	return 0;
}