NSString、NSData、char相互转换

NSString 转换成NSData 对象

NSData* newData = [@"testdata" dataUsingEncoding:NSUTF8StringEncoding]; 

NSData 转换成NSString对象

NSData * data; 
NSString *result = [[NSString alloc] initWithData:data  encoding:NSUTF8StringEncoding]; 

在iOS底层网络的开发中，会遇到NSData 转 NSString 为空的情况，原因很多，下面的解决方法是针对从服务器传过来的数据中含有非UTF-8字符(主要是UTF-8)的情况。

用libiconv清除非utf8字符
先给项目Link Binaries With Library 添加libiconv.dylib
使用如下函数对NSData进行清理，再进行转换就OK了

-(NSData *)cleanUTF8:(NSData *)data {
  iconv_t cd = iconv_open("UTF-8", "UTF-8"); // 从utf8转utf8
  int one = 1;
  iconvctl(cd, ICONV_SET_DISCARD_ILSEQ, &one); // 丢弃不正确的字符
 
  size_t inbytesleft, outbytesleft;
  inbytesleft = outbytesleft = data.length;
  char *inbuf  = (char *)data.bytes;
  char *outbuf = malloc(sizeof(char) * data.length);
  char *outptr = outbuf;
  if (iconv(cd, &inbuf, &inbytesleft, &outptr, &outbytesleft)
      == (size_t)-1) {
    NSLog(@"this should not happen, seriously");
    return nil;
  }
  NSData *result = [NSData dataWithBytes:outbuf length:data.length - outbytesleft];
  iconv_close(cd);
  free(outbuf);
  return result;
}

NSData 转换成char*

NSData *data; 
char *test=[data bytes];

char* 转换成NSData对象

byte* tempData = malloc(sizeof(byte)*16); 
NSData *content=[NSData dataWithBytes:tempData length:16];

?NSString?转?char *

1.?UTF8String

const char *cString = [string UTF8String];

2.?cStringUsingEncoding:

const char *cString = [string cStringUsingEncoding:NSUTF8StringEncoding];

3.?getCString:maxLength:encoding:

char cStringPtr[string.length * 3 + 1];
memset(cStringPtr, 0, sizeof(cStringPtr));
[string getCString:cStringPtr maxLength:sizeof(cStringPtr) encoding:NSUTF8StringEncoding];

UTF8编码需要占用3个字节，因此这里需要*3

?char*?转?NSString

1.?initWithUTF8String:

NSString *string = [[NSString alloc] initWithUTF8String:cString];

2.?initWithCString:encoding:

NSString *string = [[NSString alloc] initWithCString:cString encoding:NSUTF8StringEncoding];

3.?stringWithFormat:

NSString *string = [NSString stringWithFormat@"%s", cString];