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字符串indexOf() 和 lastIndexOf() 函数
字符串对象indexOf()函数允许你搜索字符串里的一个特殊字符的第一个例子。你也可以寻找一个补偿后的字符的第一个例子。lastIndexOf()函数使你从字符串后面开始做同样的事。
目录
简介
- 字符串indexOf() 和 lastIndexOf() 函数
- 字符串对象indexOf()函数允许你搜索字符串里的一个特殊字符的第一个例子。你也可以寻找一个补偿后的字符的第一个例子。lastIndexOf()函数使你从字符串后面开始做同样的事。
String stringOne = "";
int firstClosingBracket = stringOne.indexOf('>');
- 在这种情况下，firstClosingBracket等于5，因为第一个“>”字符在字符串的第5位（第一个字符当0数）。如果你想得到第二个最近的同类项，你可以用你知道第一个同类项的位置的事实，然后从firstClosingBracket + 1的位置开始查找，就像这样：
stringOne = "<HTML><HEAD><BODY>";
int secondClosingBracket = stringOne.indexOf('>', firstClosingBracket + 1 ); - 结果是11，位置在跟在HEAD后面。
- 如果你想从字符串的后面开始搜索，你可以用 lastIndexOf() 函数来代替。这个函数返回一个给定字符最后出现的位置。
stringOne = "<HTML><HEAD><BODY>";
int lastOpeningBracket = stringOne.lastIndexOf('<'); - 这种情况下，lastOpeningBracket等于12，“<”的位置在BODY后面。如果你想在HEAD后面第一次出现的同类项，可以用stringOne.lastIndexOf(‘<‘, lastOpeningBracket -1), 或者是第 6 个。
硬件要求
- Arduino or Genuino 开发板
电路
- 这个例子不需要连接额外的电路，除了你的开发板需要连接到你的电脑，并且打开Arduino IDE的串口监视器窗口。
样例代码
void setup() {
// Open serial communications and wait for port to open:
Serial.begin(9600);
while (!Serial) {
; // wait for serial port to connect. Needed for native USB port only
}
// send an intro:
Serial.println("\n\nString indexOf() and lastIndexOf() functions:");
Serial.println();
}
void loop() {
// indexOf() returns the position (i.e. index) of a particular character
// in a string. For example, if you were parsing HTML tags, you could use it:
String stringOne = "<HTML><HEAD><BODY>";
int firstClosingBracket = stringOne.indexOf('>');
Serial.println("The index of > in the string " + stringOne + " is " + firstClosingBracket);
stringOne = "<HTML><HEAD><BODY>";
int secondOpeningBracket = firstClosingBracket + 1;
int secondClosingBracket = stringOne.indexOf('>', secondOpeningBracket);
Serial.println("The index of the second > in the string " + stringOne + " is " + secondClosingBracket);
// you can also use indexOf() to search for Strings:
stringOne = "<HTML><HEAD><BODY>";
int bodyTag = stringOne.indexOf("<BODY>");
Serial.println("The index of the body tag in the string " + stringOne + " is " + bodyTag);
stringOne = "<UL><LI>item<LI>item<LI>item</UL>";
int firstListItem = stringOne.indexOf("<LI>");
int secondListItem = stringOne.indexOf("<LI>", firstListItem + 1);
Serial.println("The index of the second list tag in the string " + stringOne + " is " + secondListItem);
// lastIndexOf() gives you the last occurrence of a character or string:
int lastOpeningBracket = stringOne.lastIndexOf('<');
Serial.println("The index of the last < in the string " + stringOne + " is " + lastOpeningBracket);
int lastListItem = stringOne.lastIndexOf("<LI>");
Serial.println("The index of the last list tag in the string " + stringOne + " is " + lastListItem);
// lastIndexOf() can also search for a string:
stringOne = "<p>Lorem ipsum dolor sit amet</p><p>Ipsem</p><p>Quod</p>";
int lastParagraph = stringOne.lastIndexOf("<p");
int secondLastGraf = stringOne.lastIndexOf("<p", lastParagraph - 1);
Serial.println("The index of the second to last paragraph tag " + stringOne + " is " + secondLastGraf);
// do nothing while true:
while (true);
}
