Due to some protocol specifications for Quartz Composer, the string "\0\0\0" has to precede every character sent via UDP. The current value has this format: "1.23456". For the transfer the last three decimal places are not required, but the addition before every number, so it should look like this: "\0\0\01\0\0\0.\0\0\02\0\0\03". What's "the Objective-C way" to solve this?
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问题:
回答1:
If I understood you correctly, you want to send a sequence of characters (type char
). In that case,
NSString *originalString = @"1.23456";
// It's not clear if you must remove the last three digits
// so I'm assuming that the string always has the last three
// characters removed
NSUInteger stringLength = [originalString length];
if (stringLength > 3)
originalString = [originalString substringToIndex:stringLength - 3];
// I'm assuming ASCII strings so that one character maps to only one char
const char *originalCString = [originalString cStringUsingEncoding:NSASCIIStringEncoding];
if (! originalCString) {
NSLog(@"Not an ASCII string");
exit(1);
}
NSMutableData *dataToSend = [NSMutableData data];
char zeroPadding[] = { 0, 0, 0 };
NSUInteger i = 0;
char character;
while ((character = originalCString[i++])) {
[dataToSend appendBytes:zeroPadding length:sizeof zeroPadding];
[dataToSend appendBytes:&character length:1];
}
If you run
NSLog(@"%@", dataToSend);
the output should be
<00000031 0000002e 00000032 00000033>
where
00000031
means
00 00 00 31
and 31 is the ASCII code of ‘1’ (2e = ‘.’, 32 = ‘2’, 33 = ‘3’).
If you need to know the size (in bytes) of dataToSend
, use [dataToSend length]
. If you want to access the bytes themselves, use [dataToSend bytes]
.
回答2:
One variation
NSMutableData* dataToSend;
char nullLeader[] = { 0, 0, 0 };
dataToSend = [NSMutableData dataWithBytes: nullLeader length: sizeof nullLeader];
[dataToSend appendData: [myStringIWantToSend dataUsingEncoding: NSUTF8StringEncoding]];
// send the data