1.  string 转换为 NSString  

   std::string str("hello");

   NSString *str=[NSString stringWithString:str.c_str()];

   NSString *istr=[NSString stringWithString:@"zsh"];

    str=[istr cStringUsingEncoding: NSUTF8StringEncoding];
     NSString *path= [[NSBundle mainBundle]pathForResource:@"nokia" ofType:@"mp3"];

    char *tempPath=(char*)malloc(sizeof(path)+1);

    
    NSString *soundPath=[[NSBundle mainBundle] pathForResource:@mp3"]; 
    
    NSString* dirStr = [NSString stringWithFormat:@"%s",path];
    NSString* filepath = [[NSBundle mainBundle] pathForResource:dirStr ofType:nil];

    NSLog(filepath);

 2.  //NSString 转换为C 字符串

    const char* destDir = [filepath UTF8String];

   //  NSURL *soundUrl=[[NSURL alloc] initFileURLWithPath:s]; 

3.const char * to NSString

 char *str ="abc";

NSString *s = [NSString stringWithUTF8String:str];