NSString *str = nil;
// 去掉首尾空格和换行符
str = [str stringByTrimmingCharactersInSet:[NSCharacterSet whitespaceAndNewlineCharacterSet]];

// 去掉所有空格和换行符
str = [str stringByReplacingOccurrencesOfString:@"\r" withString:@""];
str = [str stringByReplacingOccurrencesOfString:@"\n" withString:@""];

如果要单独过滤左边或者右边的内容就需要自己来实现了。

可以在NSString的类目（Category）中提供如下两个方法：

// 过滤左边指定的内容
- (NSString *)stringByTrimmingLeftCharactersInSet:(NSCharacterSet *)characterSet {
    
    NSUInteger location = 0;
    NSUInteger length = [self length];
    unichar charBuffer[length];
    [self getCharacters:charBuffer];
#pragma clang diagnostic push
#pragma clang diagnostic ignored "-Wunused-value"
    for (location; location < length; location++) {
        if (![characterSet characterIsMember:charBuffer[location]]) {
            break;
        }
    }
#pragma clang diagnostic pop
    
    return [self substringWithRange:NSMakeRange(location, length - location)];
}

// 过滤右边指定的内容
- (NSString *)stringByTrimmingRightCharactersInSet:(NSCharacterSet *)characterSet {
    
    NSUInteger location = 0;
    NSUInteger length = [self length];
    unichar charBuffer[length];
    [self getCharacters:charBuffer];
#pragma clang diagnostic push
#pragma clang diagnostic ignored "-Wunused-value"
    for (length; length > 0; length--) {
        if (![characterSet characterIsMember:charBuffer[length - 1]]) {
            break;
        }
    }
#pragma clang diagnostic pop
    
    return [self substringWithRange:NSMakeRange(location, length - location)];
}

使用stringByTrimmingLeftCharactersInSet:去掉左边的空格：

NSString *str = @"   Yancy🙂  ";
str = [str stringByTrimmingLeftCharactersInSet:[NSCharacterSet whitespaceCharacterSet]];
NSLog(@"%@", str);

使用stringByTrimmingRightCharactersInSet:去掉右边的"0"：

NSString *str = @"0.012300";
str = [str stringByTrimmingRightCharactersInSet:[NSCharacterSet characterSetWithCharactersInString:@"0"]];
NSLog(@"%@", str); // 结果是0.0123