使用头文件中声明的字符串时为EXC_BAD_ACCESS

Question

I've declared a string in my header file like so:

@property (nonatomic, retain) NSString *resultOfHash;

I call my getHash method like so:

 NSString *hash = [self getHash];

My getHash method is:

-(NSString *) getHash
{
//Get username form Keychain
KeychainItemWrapper *keyChain = [[KeychainItemWrapper alloc]    initWithIdentifier:KeyChainName accessGroup:nil];
username = [keyChain objectForKey:(__bridge id)kSecAttrAccount];

//get token from NSUserDefauls
NSString *token = [[NSUserDefaults standardUserDefaults]objectForKey:@"Token"];

NSString *toHash = [[username stringByAppendingString:HashExtra] stringByAppendingString:token];

const char *s = [toHash cStringUsingEncoding:NSASCIIStringEncoding];

NSData *keyData = [NSData dataWithBytes:s length:strlen(s)];

uint8_t digest[CC_SHA1_DIGEST_LENGTH] = {0};

CC_SHA512(keyData.bytes, keyData.length, digest);

NSData *out = [NSData dataWithBytes:digest length:CC_SHA1_DIGEST_LENGTH];

//convert to string
resultOfHash = [out description];
//App crashed out above

// get rid of unwanted characters
resultOfHash = [resultOfHash stringByReplacingOccurrencesOfString:@" " withString:@""];
resultOfHash = [resultOfHash stringByReplacingOccurrencesOfString:@"<" withString:@""];
resultOfHash = [resultOfHash stringByReplacingOccurrencesOfString:@">" withString:@""];

//log to make sure it works
NSLog(@"hash is: %@", resultOfHash);

return resultOfHash;
}

My code crashes out at the line: ResultOfHash = [out description]; but I'm not sure why.

When I use a local variable the conversion works fine but then I cannot return the local variable from the getHash method. Example:

Replace ResultOfHash = [out description];

with

NSString *local = [out description];
return local;

and the conversion works fine and when I debug line by line, the debugger will go to my closing bracket on my method and then produce the EXC_BAD_ACCESS error.

I've tried running NSZombie but that didn't find anything at all.

Any help in trying to sort this out would be greatly appreciated.

Answer 1

Have a look at the answer in this question . Try converting to NSString using

[NSString *local = [[[NSString alloc] initWithData:out encoding:NSASCIIStringEncoding]; 

I haven't tested this code with this encoding, but it's similar to something I already use.

Update -

I corrected an error in the code above. I somehow left the method signiture out in a distracted copy and paste.

Answer 2

It's crashing because out is unretained. You should add retain:

resultOfHash = [[out description] retain];

or use retained property:

self.resultOfHash = [out description];

Check this, it should be work.

Answer 3

您可能需要使用NSMutableString 。

Answer 4

I think the problem is here:

uint8_t digest[CC_SHA1_DIGEST_LENGTH] = {0};
CC_SHA512(keyData.bytes, keyData.length, digest);
NSData *out = [NSData dataWithBytes:digest length:CC_SHA1_DIGEST_LENGTH];

You are using CC_SHA512 , but only allocate array of size CC_SHA1_DIGEST_LENGTH , which is smaller and will lead to the buffer overrunning.

To correct this, you should use CC_SHA512_DIGEST_LENGTH instead.