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How does the C/C++ compiler manipulate the escape character ["\"] in source code? How is compiler grammar written for processing that character? What does the compiler do after encountering that character?
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It is used in representing certain whitespace characters: "\t" is a tab, "\n" is a newline, and "\r" is a carriage return.
In computing and telecommunication, an escape character is a character that invokes an alternative interpretation on the following characters in a character sequence. An escape character is a particular case of metacharacters.
As we've seen, a backslash \ is used to denote character classes, e.g. \d . So it's a special character in regexps (just like in regular strings).
Most compilers are divided into parts: the compiler front-end is called a lexical analyzer or a scanner. This part of the compiler reads the actual characters and creates tokens. It has a state machine which decides, upon seeing an escape character, whether it is genuine (for example when it appears inside a string) or it modifies the next character. The token is output accordingly as the escape character or some other token (such as a tab or a newline) to the next part of the compiler (the parser). The state machine can group several characters into a token.
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An interesting note on this subject is On Trusting Trust [PDF link].
The paper describes one way a compiler could handle this problem exactly, shows how the c-written-in-c compiler does not have an explicit translation of the codes into ASCII values; and how to bootstrap a new escape code into the compiler so that the understanding of the ASCII value for the new code is also implicit.
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