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;
}