iOS-NSString常见方法

</pre><pre name="code" class="html">#import <Foundation/Foundation.h>

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

        // 1、创建NSString 方法1
        NSString *str1 = @"abc";
        NSLog(@"str addr %p  val is %@ ",str1,str1);

        // 2、格式化创建NSString
            //字符串常量区
        NSString *str2 =[NSString stringWithFormat:@"%@",@"ABCD"];
        NSLog(@"str addr %p  val is %@ ",str2,str2);
        char buffer[200] ={'a','b','c','d'};
        NSString *str3 =[NSString stringWithFormat:@"%s",buffer];
        NSLog(@"str addr %p  val is %@ ",str3,str3);
            //堆区
        char buffer1[200] ={'a','b','c','d'};
        NSString *str4 =[[NSString alloc] initWithFormat:@"%s",buffer1];
        NSLog(@"str addr %p  val is %@ ",str4,str4);

        // 3、写入到文件中区
        NSString *str5 = @"I LOVE YOU ";
        NSError *err;

        [str5 writeToFile:@"/Users/yangsanchao/Desktop/test.txt" atomically:YES encoding:NSUTF8StringEncoding error:&err];
        //************* 从文件中读取字符串显示到控制台上 ***************
        NSString *str6 = [ NSString stringWithContentsOfFile:@"/Users/yangsanchao/Desktop/test.txt" encoding:NSUTF8StringEncoding error:&err];
        if (err == nil){
            NSLog(@"文件读取成功 %@ ",str6);

        } else {
            NSLog(@"file read faile %@",err);
        }

        //5> NSString的常见方法:
        //5.1  - (NSString *)uppercaseString; 大写转小写
        //     - (NSString *)lowercaseString;小写转大写 I LOVE YOU TOO"
        NSString *str7 = @"i love you";
        NSString *str8 = @"i love you too ; I LOVE YOU TOO ";
        NSLog(@"小写转大写 %@ ",[str7 uppercaseString]);
        NSLog(@"大写转小写 %@ ",[str8 lowercaseString]);
        NSLog(@"首字母大写 %@ ",[str7 capitalizedString]);//首字母大写
        NSLog(@"是否相等 %d",[str7 isEqualTo:str7]);

        /*逐字符比较大小；s1>s2: 1;     s1=s2: 0 ;   s1<s2: -1*/
        NSLog(@"逐字符比较大小 %ld",[str8 compare:str7]);
        NSLog(@"逐字符比较大小 %ld",[str7 compare:str8]);

        NSLog(@"是否以xx开头 %d",[str7 hasPrefix:@"i"]);
        NSLog(@"是否以xx结尾 %d",[str7 hasSuffix:@"you"]);

        //读取NSRange 方法1
        NSRange range  =  [str7 rangeOfString:@"you"];
        NSLog(@"读取NSRange 方法1 %lu %lu",range.location,range.length);
        //读取NSRange 方法2
        NSLog(@"NSRange 方法2 %@",NSStringFromRange([str7 rangeOfString:@"you"]));
        //NSRange  range1 = [str7 rangeOfString:@"you" options NSBackwardsSearch];
        NSLog(@"反方向搜索: %@", NSStringFromRange([str7 rangeOfString:@"you" options: NSBackwardsSearch]));

        NSLog(@"从指定位置from开始%@",[str7 substringFromIndex:0]);
        NSLog(@"从指定位置to开始%@",[str7 substringToIndex:6]);

        NSLog(@"截取%@",[str7 substringWithRange: NSMakeRange(5, 3)]);
        //NSLog(@"截取%@",[str7 substringWithRange: {5,4}]);
        NSLog(@"替换%@",[str7 stringByReplacingOccurrencesOfString:@"you"
                                                      withString:@"myself"]);
        //长度
        NSLog(@"字符长度 %lu",str7.length);//.
        NSLog(@"字符长度 %lu",[str7 length]);//对象调用
        NSLog(@"某个字符 %c ",[str7 characterAtIndex:0]);
        /*
         - (double)doubleValue;
         - (float)floatValue;
         - (int)intValue;
         - (char *)UTF8String;
         */
        NSString *s1 = @"123";
        double du = s1.doubleValue;
        float fl  = s1.floatValue;
        int i = s1.intValue;
        const char *s2 = s1.UTF8String;

        printf("du:%.2f fl:%.2f i:%d s2:%s \n",du,fl,i,s2);

    }
    return 0;
}