Foundation之NSString

一、NSString的创建

int main(int argc, const char * argv[])
{

    @autoreleasepool {
        
        //这种方式不需要release
        NSString *s1 = @"this is a string";
        NSLog(@"s1=%@", s1);
        
        //这种方式需要release
        NSString *s2 = [[NSString alloc] init];
        s2 = @"this is a string";
        NSLog(@"s2=%@", s2);
        [s2 release];
        
        //这种方式需要release
        NSString *s3 = [[NSString alloc] initWithString:@"this is a string"];
        NSLog(@"s3=%@", s3);
        [s3 release];
        //这种方式不需要release
        s3 = [NSString stringWithString:@"this is a string"];
        NSLog(@"s3=%@", s3);
        
        //这种方式需要release
        NSString *s4 = [[NSString alloc] initWithUTF8String:"this is a string"];
        NSLog(@"s4=%@", s4);
        [s4 release];
        //这种方式不需要release
        s4 = [NSString stringWithUTF8String:"this is a string"];
        NSLog(@"s4=%@", s4);
        
        //这种方式需要release
        NSString *s5 = [[NSString alloc] initWithFormat:@"my age is %i and height is %.2f", 18, 1.7f];
        NSLog(@"s5=%@", s5);
        [s5 release];
        //这种方式不需要release
        s5 = [NSString stringWithFormat:@"my age is %i and height is %.2f", 18, 1.7f];
        NSLog(@"s5=%@", s5);
        
    }
    return 0;
}

二、NSString的常用方法

int main(int argc, const char * argv[])
{

    @autoreleasepool {
        
        NSString *s1 = @"This is a String";
        // 转大写
        NSLog(@"%@", [s1 uppercaseString]); //THIS IS A STRING
        // 转小写
        NSLog(@"%@", [s1 lowercaseString]); //this is a string
        // 每个单词的首字母转大写
        NSLog(@"%@", [s1 capitalizedString]); //This Is A String
        
        // 比较两个字符串的内容是否相同
        BOOL r1 = [@"abc" isEqualToString:@"Abc"];
        NSLog(@"%i", r1); //0
        
        // 逐个字符进行比较大小
        NSComparisonResult r2 = [@"abc" compare:@"Abc"];
        if (r2==NSOrderedSame) {
            NSLog(@"两个字符串的内容相同");
        } else if (r2==NSOrderedAscending) {
            NSLog(@"右边 > 左边");
        } else if (r2==NSOrderedDescending) {
            NSLog(@"右边 < 左边");
        }
        
        // 是否以This开头
        BOOL r3 = [s1 hasPrefix:@"This"];
        NSLog(@"%i", r3); //1
        // 是否以String结尾
        BOOL r4 = [s1 hasSuffix:@"String"];
        NSLog(@"%i", r4); //1
        
        // 查找is在s1中的位置，
        NSRange r5 = [s1 rangeOfString:@"is"];
        if (r5.location == NSNotFound) {
            NSLog(@"找不到");
        } else {
            NSLog(@"%@", NSStringFromRange(r5)); //{2, 2}
        }
        
        // 从尾部查找is在s1中的位置，
        NSRange r6 = [s1 rangeOfString:@"is" options:NSBackwardsSearch];
        if (r6.location == NSNotFound) {
            NSLog(@"找不到");
        } else {
            NSLog(@"%@", NSStringFromRange(r6)); //{5, 2}
        }
        
        // 从索引3开始截取到末尾
        NSLog(@"%@", [@"123456" substringFromIndex:3]); //456
        // 从头部截取到索引3之前
        NSLog(@"%@", [@"123456" substringToIndex:3]); //123
        // 指定范围截取
        NSLog(@"%@", [@"123456" substringWithRange:NSMakeRange(2, 3)]); //345
        
        // 分隔字符串
        NSArray *arr = [@"1,2,3,4,5" componentsSeparatedByString:@","];
        NSLog(@"%@", arr[2]); //3
        
        // 字符串长度
        NSLog(@"%zi", [@"abc" length]); //3
        // 转为int
        NSLog(@"%i", [@"12" intValue]);
    
    }
    return 0;
}

三、从文件中读取文本

int main(int argc, const char * argv[])
{

    @autoreleasepool {
        
        NSString *path = @"/Users/Lane/Desktop/test.txt";
        
        NSError *error;
        
        NSString *s1 = [NSString stringWithContentsOfFile:path encoding:NSUTF8StringEncoding error:&error];
        
        if (error) {
            NSLog(@"文件读取失败: %@", error);
        } else {
            NSLog(@"%@", s1);
        }
        
        
    }
    return 0;
}

四、从URL中读取文本

int main(int argc, const char * argv[])
{

    @autoreleasepool {
        
        NSURL *url = [NSURL URLWithString:@"http://www.baidu.com"];
        
        NSError *error;
        
        NSString *s1 = [NSString stringWithContentsOfURL:url encoding:NSUTF8StringEncoding error:&error];
        
        if (error) {
            NSLog(@"URL读取失败: %@", error);
        } else {
            NSLog(@"%@", s1);
        }
        
        
    }
    return 0;
}

五、写入文本文件

int main(int argc, const char * argv[])
{

    @autoreleasepool {
        
        NSString *path = @"/Users/Lane/Desktop/test2.txt";
        
        NSError *error;
        
        NSString *s1 = @"123456";
        [s1 writeToFile:path atomically:YES encoding:NSUTF8StringEncoding error:&error];
        
        if (error) {
            NSLog(@"文件写入失败: %@", error);
        } else {
            NSLog(@"文件写入成功");
        }
        
        
    }
    return 0;
}