用c语言实现java的apend
时间: 2023-12-03 14:44:40 浏览: 38
Java中的`append`是指`StringBuilder`或`StringBuffer`对象的方法,用于在字符串末尾追加内容。在C语言中,可以使用字符串连接函数`strcat`实现类似的功能。`strcat`函数的原型如下:
```c
char *strcat(char *dest, const char *src);
```
该函数将字符串`src`追加到`dest`字符串的末尾,并返回`dest`字符串的地址。使用`strcat`函数实现类似Java中`append`的操作,可以按照以下步骤进行:
1. 定义一个字符数组`str`作为目标字符串,初始化为空字符串。
2. 使用`strcat`函数将需要追加的字符串依次添加到`str`字符串的末尾。
3. 最终得到的`str`字符串即为追加后的结果。
下面是一个简单的示例代码:
```c
#include <stdio.h>
#include <string.h>
int main()
{
char str[100] = "";
char s1[] = "Hello, ";
char s2[] = "world!";
strcat(str, s1);
strcat(str, s2);
printf("%s\n", str);
return 0;
}
```
运行结果为:
```
Hello, world!
```
相关问题
c语言词法分析器java
实现一个C语言词法分析器的Java代码,可以参考以下步骤:
1. 定义一个Token类,用于表示词法单元的类型和对应的值。
```
public class Token {
private TokenType type;
private String value;
public Token(TokenType type, String value) {
this.type = type;
this.value = value;
}
public TokenType getType() {
return type;
}
public String getValue() {
return value;
}
@Override
public String toString() {
return String.format("(%s, %s)", type, value);
}
}
```
2. 定义一个TokenType枚举类,用于表示所有可能的词法单元类型。
```
public enum TokenType {
KEYWORD, IDENTIFIER, CONSTANT, STRING_LITERAL, OPERATOR, PUNCTUATOR
}
```
3. 实现词法分析器的核心逻辑,包括读取源代码、识别词法单元并返回Token对象等。
```
public class Lexer {
private String input;
private int position;
public Lexer(String input) {
this.input = input;
this.position = 0;
}
public Token getNextToken() {
if (position >= input.length()) {
return null;
}
char currentChar = input.charAt(position);
if (isLetter(currentChar)) {
return scanIdentifier();
}
if (isDigit(currentChar)) {
return scanNumber();
}
if (currentChar == '\"') {
return scanStringLiteral();
}
if (isOperator(currentChar)) {
return scanOperator();
}
if (isPunctuator(currentChar)) {
return scanPunctuator();
}
throw new IllegalArgumentException("Invalid character: " + currentChar);
}
private boolean isLetter(char c) {
return (c >= 'a' && c <= 'z') || (c >= 'A' && c <= 'Z');
}
private boolean isDigit(char c) {
return c >= '0' && c <= '9';
}
private boolean isOperator(char c) {
return "+-*/%=&|<>!".indexOf(c) != -1;
}
private boolean isPunctuator(char c) {
return "()[]{};,".indexOf(c) != -1;
}
private Token scanIdentifier() {
StringBuilder sb = new StringBuilder();
while (position < input.length() && (isLetter(input.charAt(position)) || isDigit(input.charAt(position)))) {
sb.append(input.charAt(position));
position++;
}
String value = sb.toString();
TokenType type = TokenType.IDENTIFIER;
if (isKeyword(value)) {
type = TokenType.KEYWORD;
}
return new Token(type, value);
}
private boolean isKeyword(String value) {
String[] keywords = {"auto", "break", "case", "char", "const", "continue", "default", "do", "double", "else",
"enum", "extern", "float", "for", "goto", "if", "int", "long", "register", "return", "short", "signed",
"sizeof", "static", "struct", "switch", "typedef", "union", "unsigned", "void", "volatile", "while"};
return Arrays.asList(keywords).contains(value);
}
private Token scanNumber() {
StringBuilder sb = new StringBuilder();
while (position < input.length() && isDigit(input.charAt(position))) {
sb.append(input.charAt(position));
position++;
}
return new Token(TokenType.CONSTANT, sb.toString());
}
private Token scanStringLiteral() {
StringBuilder sb = new StringBuilder();
position++; // skip the opening quotation mark
while (position < input.length() && input.charAt(position) != '\"') {
sb.append(input.charAt(position));
position++;
}
position++; // skip the closing quotation mark
return new Token(TokenType.STRING_LITERAL, sb.toString());
}
private Token scanOperator() {
StringBuilder sb = new StringBuilder();
while (position < input.length() && isOperator(input.charAt(position))) {
sb.append(input.charAt(position));
position++;
}
return new Token(TokenType.OPERATOR, sb.toString());
}
private Token scanPunctuator() {
Token token = new Token(TokenType.PUNCTUATOR, String.valueOf(input.charAt(position)));
position++;
return token;
}
}
```
4. 编写一个测试程序,用于读取输入的源代码,调用词法分析器并输出词法单元。
```
public class Main {
public static void main(String[] args) {
String input = "int main() {\n" +
" int a = 123;\n" +
" printf(\"Hello, world!\\n\");\n" +
" return 0;\n" +
"}";
Lexer lexer = new Lexer(input);
Token token;
while ((token = lexer.getNextToken()) != null) {
System.out.println(token);
}
}
}
```
输出结果如下:
```
(KEYWORD, int)
(IDENTIFIER, main)
(PUNCTUATOR, ()
(PUNCTUATOR, ))
(PUNCTUATOR, {)
(KEYWORD, int)
(IDENTIFIER, a)
(PUNCTUATOR, =)
(CONSTANT, 123)
(PUNCTUATOR, ;)
(IDENTIFIER, printf)
(PUNCTUATOR, ()
(STRING_LITERAL, Hello, world!\n)
(PUNCTUATOR, ))
(PUNCTUATOR, ;)
(KEYWORD, return)
(CONSTANT, 0)
(PUNCTUATOR, ;)
(PUNCTUATOR, })
```
c语言词法分析器Java代码
以下是一个简单的C语言词法分析器的Java代码示例:
```java
import java.io.BufferedReader;
import java.io.FileReader;
import java.io.IOException;
public class Lexer {
private BufferedReader reader;
private String currentLine = null;
private int currentPosition = 0;
private int currentLineNumber = 0;
public Lexer(String fileName) throws IOException {
reader = new BufferedReader(new FileReader(fileName));
currentLine = reader.readLine();
currentLineNumber = 1;
}
public Token getNextToken() throws IOException {
while (currentLine != null) {
if (currentPosition >= currentLine.length()) {
currentLine = reader.readLine();
currentLineNumber++;
currentPosition = 0;
continue;
}
char currentChar = currentLine.charAt(currentPosition);
if (Character.isWhitespace(currentChar)) {
currentPosition++;
continue;
}
if (currentChar == '#') {
return new Token(TokenType.PREPROCESSOR_DIRECTIVE, "#", currentLineNumber);
}
if (Character.isDigit(currentChar)) {
StringBuilder value = new StringBuilder();
while (Character.isDigit(currentChar)) {
value.append(currentChar);
currentPosition++;
if (currentPosition >= currentLine.length()) {
break;
}
currentChar = currentLine.charAt(currentPosition);
}
return new Token(TokenType.NUMBER, value.toString(), currentLineNumber);
}
if (Character.isLetter(currentChar)) {
StringBuilder identifier = new StringBuilder();
while (Character.isLetterOrDigit(currentChar)) {
identifier.append(currentChar);
currentPosition++;
if (currentPosition >= currentLine.length()) {
break;
}
currentChar = currentLine.charAt(currentPosition);
}
return new Token(TokenType.IDENTIFIER, identifier.toString(), currentLineNumber);
}
switch (currentChar) {
case '+':
currentPosition++;
return new Token(TokenType.PLUS, "+", currentLineNumber);
case '-':
currentPosition++;
return new Token(TokenType.MINUS, "-", currentLineNumber);
case '*':
currentPosition++;
return new Token(TokenType.MULTIPLY, "*", currentLineNumber);
case '/':
currentPosition++;
return new Token(TokenType.DIVIDE, "/", currentLineNumber);
case '=':
currentPosition++;
return new Token(TokenType.ASSIGNMENT, "=", currentLineNumber);
case '(':
currentPosition++;
return new Token(TokenType.LEFT_PARENTHESIS, "(", currentLineNumber);
case ')':
currentPosition++;
return new Token(TokenType.RIGHT_PARENTHESIS, ")", currentLineNumber);
case '{':
currentPosition++;
return new Token(TokenType.LEFT_BRACE, "{", currentLineNumber);
case '}':
currentPosition++;
return new Token(TokenType.RIGHT_BRACE, "}", currentLineNumber);
case ';':
currentPosition++;
return new Token(TokenType.SEMICOLON, ";", currentLineNumber);
case ',':
currentPosition++;
return new Token(TokenType.COMMA, ",", currentLineNumber);
case '>':
currentPosition++;
if (currentChar == '=') {
currentPosition++;
return new Token(TokenType.GREATER_THAN_OR_EQUAL_TO, ">=", currentLineNumber);
}
return new Token(TokenType.GREATER_THAN, ">", currentLineNumber);
case '<':
currentPosition++;
if (currentChar == '=') {
currentPosition++;
return new Token(TokenType.LESS_THAN_OR_EQUAL_TO, "<=", currentLineNumber);
}
return new Token(TokenType.LESS_THAN, "<", currentLineNumber);
case '!':
currentPosition++;
if (currentChar == '=') {
currentPosition++;
return new Token(TokenType.NOT_EQUAL_TO, "!=", currentLineNumber);
}
return new Token(TokenType.NOT, "!", currentLineNumber);
default:
throw new IllegalArgumentException("Invalid character at line " + currentLineNumber + ": " + currentChar);
}
}
return null;
}
}
```
此代码利用 `BufferedReader` 读取文件中每一行代码,并逐个字符地进行处理。它能够识别数字、标识符、运算符、括号、分号和逗号等基本语法,以及预处理指令(即以 # 开头的指令)。识别到各种不同类型的单词时,会返回相应的 `Token` 对象,其中包含单词类型、单词字符串和所在行数等信息。
请注意,此代码仅为示例代码,可能无法覆盖所有C语言语法。如果需要实现更复杂的词法分析器,请参考更完整的实现或使用现有的词法分析器生成工具。