做一个类别吧，以后用来很方便。代码如下：
.h
#import <Foundation/Foundation.h>
@interface NSString (Additions)
- (NSString *) MD5;
@end
.m
#import "NSString+Additions.h"
#import <sys/xattr.h>
#import <CommonCrypto/CommonDigest.h>
@implementation NSString (Additions)
- (NSString *) MD5 {
// Create pointer to the string as UTF8
const char* ptr = [self UTF8String];
unsigned char md5Buffer[CC_MD5_DIGEST_LENGTH];
// Create 16 byte MD5 hash value, store in buffer
CC_MD5(ptr, (CC_LONG)strlen(ptr), md5Buffer);
// Convert MD5 value in the buffer to NSString of hex values
NSMutableString* output = [NSMutableString stringWithCapacity:CC_MD5_DIGEST_LENGTH * 2];
for (int i = 0; i < CC_MD5_DIGEST_LENGTH; i++) {
[output appendFormat:@"%02x",md5Buffer[i]];
}
return output;
}
@end
