NSString中怎么转换为char类型

#import <Foundation/Foundation.h>

int main(int argc, const char * argv[]) {
    @autoreleasepool {
        
        NSString * str= @"abcdefghijklmn";
        char ch = [str characterAtIndex:6];//提取下标为6的字符给ch
        const char *cc = [str UTF8String];//转换成C字符串
        printf("%c\n%s\n",ch,cc);
        
    }
    return 0;
}
-----------------------------
g
abcdefghijklmn
Program ended with exit code: 0