objective-c - 如何将数据附加到 Cocoa 中的 NSmutableData

Question

我想添加新的 NSdata = x20 (ASCII) ，它最后是 NSMutableData 中的一个空格，以足够固定的再见。示例:NSmuatabledata 有 400 字节，但我需要这个 NSMutableData 有 600 字节。所以我想在这个 nsmutableData 最后添加 200 个字节(十六进制 x20)。我怎样才能做到这一点？请帮我。提前致谢

// write xmlDoc to file
NSData* xmlData = [xmlDoc XMLDataWithOptions:NSXMLNodePreserveAll];
NSLog(@"xmlData %@",xmlData);
NSMutableData * datawrite = [xmlData mutableCopy ] ;
NSArray *array = [[NSArray alloc] init]; // i dont know how to add x20 (hex) to this array 
[datawrite appendData:[[NSString stringWithFormat:@"%@", array] dataUsingEncoding:NSUTF8StringEncoding]];

Answer 1

NSMutableData *datawrite = ...
NSUInteger oldLength = [datawrite length];
NSUInteger newLength = 600;
if (newLength > oldLength ) {
    // extend mutable data object:
    [datawrite setLength:newLength];

    // fill appended bytes with space characters:
    char *bytes = [datawrite mutableBytes];
    memset(bytes + oldLength, ' ', newLength - oldLength);
}