“implicit declaration of function” error in Objective-C

Question

i want to convert a short string to md5 hash , I found several post about it but noone worked. it's the simplest example that I found . i have this error

implicit declaration of function CC_MD5 is invalid in C99

- (NSString *) md5:(NSString *) input
{
 const char *cStr = [input UTF8String];
 unsigned char digest[16];
 CC_MD5( cStr, strlen(cStr), digest ); // This is the md5 call

 NSMutableString *output = [NSMutableString stringWithCapacity:CC_MD5_DIGEST_LENGTH * 2];

 for(int i = 0; i < CC_MD5_DIGEST_LENGTH; i++)
 [output appendFormat:@"%02x", digest[i]];

 return  output;
 }

UPDATE i added #import , it work fine when i call the method like this :

[self md5:@"admin"];

, i get the right md5 hash. But when i do this

 [self md5:userId];

i get an error ,

[NSDecimalNumber UTF8String]: unrecognized selector sent to instance 0x4d3e280 But userId is not decimal , he contain facebook id , but it's declared as NSString

NSString *userId;
@property(retain,nonatomic) NSString *userId;

Answer 1

Because the declaration of CC_MD5 has not been seen.

Include the security framework in your project and

#import <CommonCrypto/CommonDigest.h>

Answer 2

您需要在定义了MD5函数的类顶部包括Crypto库中的CommonDigest Header文件，并包括安全框架

#import <CommonCrypto/CommonDigest.h>

Answer 3

您是否正在导入定义CC_MD5的正确接口？

#import "CommonDigest.h"