Null result on Converting NSData to NSString

问题

I am facing a problem when converting NSData to NSString. I'm using UTF8Enconding but the result is null!!

Here is the data I receive <100226ab c0a8010b 00000000 00000000> it must be either 192.168.1.11 or 192.168.1.17.

This is the method I use to convert :

 NSString *ipAddress = [[NSString alloc] initWithData:address encoding:NSUTF8StringEncoding];

Is there anything wrong?!

By the way, This the did receive data delegate of GCDAsyncUdpSocket library.

回答1:

From the documentation of GCDAsyncUdpSocket:

The localAddress method returns a sockaddr structure wrapped in a NSData object.

The following code unwraps the data to a sockaddr structure and converts the IP address to a NSString. It works with IPv4 and IPv6 addresses.

#include <sys/socket.h>
#include <netdb.h>

NSData *data = ...; // your data
NSLog(@"data = %@", data);

// Copy data to a "sockaddr_storage" structure.
struct sockaddr_storage sa;
socklen_t salen = sizeof(sa);
[data getBytes:&sa length:salen];

// Get host from socket address as C string:
char host[NI_MAXHOST];
getnameinfo((struct sockaddr *)&sa, salen, host, sizeof(host), NULL, 0, NI_NUMERICHOST);

// Convert C string to NSString:
NSString *ipAddress = [[NSString alloc] initWithBytes:host length:strlen(host) encoding:NSUTF8StringEncoding];
NSLog(@"strAddr = %@", ipAddress);

Output:

data = <100226ab c0a8010b 00000000 00000000>
strAddr = 192.168.1.11

回答2:

This is not a string response. This is binary data. If you consider <100226ab c0a8010b 00000000 00000000>, look at the coa8010b: c0 in hex is equal to 192 in decimal, a8 = 168, 01 = 1, and 0b = 11. In short, this is a binary representation, not a string representation, of 192.168.1.11.

You may want to more carefully examine the GCDAsyncUdpSocket documentation for the nature of response you should get, as it's apparently binary data, not a string.

回答3:

I guess there is problem with the encoding . I have also faced similar issue and solved by:

NSString *responseString =[[NSString alloc] initWithBytes:[data bytes] length:[data length] encoding:NSUnicodeStringEncoding];

回答4:

Found a much quicker way to do it, using inet_ntoa():

//Get the bytes from the data and cast it to the correct struct
struct sockaddr_in *addr = (struct sockaddr_in *)[address bytes];
//inet_ntoa converts from the binary format to a C string
NSString *IP = [NSString stringWithCString:inet_ntoa(addr->sin_addr) encoding:NSASCIIStringEncoding];

回答5:

First try with other encoding formats available

 1. NSASCIIStringEncoding
 2. NSMacOSRomanStringEncoding
 3. NSShiftJISStringEncoding.

even if it not works,try like the following ways

 1. NSData *data = [NSData dataWithContentsOfURL:URL];
// Assuming data is in UTF8.
NSString *string = [NSString stringWithUTF8String:[data bytes]];

 2. This is like as you done.

// if data is in another encoding, for example ISO-8859-1
NSString *string = [[NSString alloc]
            initWithData:data encoding: NSISOLatin1StringEncoding];

来源：https://stackoverflow.com/questions/14037129/null-result-on-converting-nsdata-to-nsstring

标签

objective-c

ios

asyncsocket