ASCII ：（American Standard Code for Information Interchange，美国标准信息交换代码）
Unicode：Unicode 是为了解决传统的字符编码方案的局限而产生的，它为每种语言中的每个字符设定了统一并且唯一的二进制编码，以满足跨语言、跨平台进行文本转换、处理的要求。
UTF-8 （UTF）：是UnicodeTransformationFormat的缩写，意为Unicode转换格式,是一种中间格式的字符集。
GB2312（GBK）：GB2312 也是ANSI编码里的一种，对ANSI编码最初始的ASCII编码进行扩充，为了满足国内在计算机中使用汉字的需要，中国国家标准总局发布了一系列的汉字字符集国家标准编码，统称为GB码，或国标码。其中最有影响的是于1980年发布的《信息交换用汉字编码字符集 基本集》，标准号为GB 2312-1980,因其使用非常普遍，也常被通称为国标码。GB2312编码通行于我国内地；新加坡等地也采用此编码。几乎所有的中文系统和国际化的软件都支持GB 2312。
Base64：是网络上最常见的用于传输8Bit字节代码的编码方式之一,可用于在HTTP环境下传递较长的标识信息。
常用编码间转化：
//Unicode转UTF-8
NSString *unicodeStr = self;
NSString *tempStr1 = [unicodeStr stringByReplacingOccurrencesOfString:@"\\u" withString:@"\\U"];
NSString *tempStr2 = [tempStr1 stringByReplacingOccurrencesOfString:@"\"" withString:@"\\\""];
NSString *tempStr3 = [[@"\"" stringByAppendingString:tempStr2] stringByAppendingString:@"\""];
NSData *tempData = [tempStr3 dataUsingEncoding:NSUTF8StringEncoding];
NSString* returnStr = [NSPropertyListSerialization propertyListFromData:tempData
mutabilityOption:NSPropertyListImmutable
format:NULL
errorDescription:NULL];
return [returnStr stringByReplacingOccurrencesOfString:@"\\r\\n" withString:@"\n"];
}
//UTF-8转Unicode
> ``` +(NSString *) utf8ToUnicode:(NSString *)string
{
NSUInteger length = [string length];
NSMutableString *s = [NSMutableString stringWithCapacity:0];
for (int i = 0;i < length; i++)
{
unichar _char = [string characterAtIndex:i];
//判断是否为英文和数字
if (_char <= '9' && _char >= '0')
{
[s appendFormat:@"%@",[string substringWithRange:NSMakeRange(i, 1)]];
}
else if(_char >= 'a' && _char <= 'z')
{
[s appendFormat:@"%@",[string substringWithRange:NSMakeRange(i, 1)]];
}
else if(_char >= 'A' && _char <= 'Z')
{
[s appendFormat:@"%@",[string substringWithRange:NSMakeRange(i, 1)]];
}
else
{
[s appendFormat:@"\\u%x",[string characterAtIndex:i]];
}
}
return s;
}
// NSString to ASCII
int asciiCode = [string characterAtIndex:0]; // 65```
// ASCII to NSString
NSString *string = [NSString stringWithFormat:@"%c", asciiCode]; // A```
一些常用的场景转换：
// url encode
CFStringRef sRef = CFURLCreateStringByAddingPercentEscapes(NULL,
(CFStringRef)self,
NULL,
(CFStringRef)@"!*'\"();:@&=+$,/?%#[]% ",
CFStringConvertNSStringEncodingToEncoding(encoding));
NSString *re = [NSString stringWithFormat:@"%@",sRef];
CFRelease(sRef);
return re;
}
> ```
-(NSString *)urlEncodeWithEncodingUTF8{
return [self urlEncodeUsingEncoding:NSUTF8StringEncoding];
}```
// unicode decode
> ```
-(NSString *)unicodeDecodeString{
NSString *unicodeStr = self;
NSString *tempStr1 = [unicodeStr stringByReplacingOccurrencesOfString:@"\\u" withString:@"\\U"];
NSString *tempStr2 = [tempStr1 stringByReplacingOccurrencesOfString:@"\"" withString:@"\\\""];
NSString *tempStr3 = [[@"\"" stringByAppendingString:tempStr2] stringByAppendingString:@"\""];
NSData *tempData = [tempStr3 dataUsingEncoding:NSUTF8StringEncoding];
NSString* returnStr = [NSPropertyListSerialization propertyListFromData:tempData
mutabilityOption:NSPropertyListImmutable
format:NULL
errorDescription:NULL];
return [returnStr stringByReplacingOccurrencesOfString:@"\\r\\n" withString:@"\n"];
}
常用的加密算法
//MD5
-(NSString *) md5 { const char *cStr = [self UTF8String]; unsigned char digest[CC_MD5_DIGEST_LENGTH]; CC_MD5( cStr, (CC_LONG)strlen(cStr), digest ); 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; }
//sha1
- (NSString*) sha1 { const char *cstr = [self cStringUsingEncoding:NSUTF8StringEncoding]; NSData *data = [NSData dataWithBytes:cstr length:self.length];
uint8_t digest[CC_SHA1_DIGEST_LENGTH];
CC_SHA1(data.bytes, (CC_LONG)data.length, digest);
NSMutableString* output = [NSMutableString stringWithCapacity:CC_SHA1_DIGEST_LENGTH * 2];
for(int i = 0; i < CC_SHA1_DIGEST_LENGTH; i++) [output appendFormat:@"%02x", digest[i]];
return output;
}
//sha1_base64
- (NSString *) sha1_base64 {
const char *cstr = [self cStringUsingEncoding:NSUTF8StringEncoding];
NSData *data = [NSData dataWithBytes:cstr length:self.length];
uint8_t digest[CC_SHA1_DIGEST_LENGTH]; CC_SHA1(data.bytes, (CC_LONG)data.length, digest); NSData * base64 = [[NSData alloc]initWithBytes:digest length:CC_SHA1_DIGEST_LENGTH]; base64 = [GTMBase64 encodeData:base64]; NSString * output = [[NSString alloc] initWithData:base64 encoding:NSUTF8StringEncoding]; return output; }
//md5_base64
- (NSString *) md5_base64 {
const char *cStr = [self UTF8String]; unsigned char digest[CC_MD5_DIGEST_LENGTH]; CC_MD5( cStr, (CC_LONG)strlen(cStr), digest ); NSData * base64 = [[NSData alloc]initWithBytes:digest length:CC_MD5_DIGEST_LENGTH]; base64 = [GTMBase64 encodeData:base64]; NSString * output = [[NSString alloc] initWithData:base64 encoding:NSUTF8StringEncoding]; return output; }
//base64
NSData * data = [self dataUsingEncoding:NSASCIIStringEncoding allowLossyConversion:YES];
data = [GTMBase64 encodeData:data];
NSString * output = [[NSString alloc] initWithData:data encoding:NSUTF8StringEncoding];
return output;
}