Implicit conversion loses integer precision in ZLib compression method

Implicit conversion loses integer precision: 'unsigned long' to 'uInt' (aka 'unsigned int')

I am trying to update my application from 32bit to 64bit, since changing the architecture I have recived an error as decribed above.

I have a method that takes NSData that is zlib compressed and returns the decomrepssed data.

This is the method.

- (NSData*) dataByDecompressingData:(NSData*)data {

     NSLog(@"%lu", (unsigned long)data.length);

    Byte* bytes = (Byte*)[data bytes];
    NSInteger len = [data length];
    NSMutableData *decompressedData = [[NSMutableData alloc] initWithCapacity:COMPRESSION_BLOCK];
    Byte* decompressedBytes = (Byte*) malloc(COMPRESSION_BLOCK);

    z_stream stream;
    int err;
    stream.zalloc = (alloc_func)0;
    stream.zfree = (free_func)0;
    stream.opaque = (voidpf)0;

    stream.next_in = bytes;
    err = inflateInit(&stream);
    CHECK_ERR(err, @"inflateInit");

    while (true) {
        stream.avail_in = len - stream.total_in; // this is where the error happens the yellow triangle is under the "minus" -
        stream.next_out = decompressedBytes;
        stream.avail_out = COMPRESSION_BLOCK;
        err = inflate(&stream, Z_NO_FLUSH);
        [decompressedData appendBytes:decompressedBytes length:(stream.total_out-[decompressedData length])];
        if(err == Z_STREAM_END)
            break;
        CHECK_ERR(err, @"inflate");
    }

    err = inflateEnd(&stream);
    CHECK_ERR(err, @"inflateEnd");

    free(decompressedBytes);
    return decompressedData;
}

I am not sure how to fix this. I have tried to type cast len using (int) however this still dose not work. .

Solution

That's not an error, it's a warning. And if you'd like to silence it, you can simply cast the unsigned long portion of your expression to an unsigned int:

stream.avail_in = (uint)(len - stream.total_in);

The warning simply alerts you to the fact that you're turning a long into an int, thus losing precision; and since you haven't explicitly cast your long into an int, your compiler's just letting you know that maybe you're losing precision unintentionally.