Document exceptions to the rules for parsing C arguments

docs/c-language/parsing-c-command-line-arguments.md

@@ -1,7 +1,8 @@
 ---
 title: "Parsing C Command-Line Arguments"
-ms.date: "11/04/2016"
-helpviewer_keywords: ["quotation marks, command-line arguments", "double quotation marks", "command line, parsing", "parsing, command-line arguments", "startup code, parsing command-line arguments"]
+description: "Learn how the Microsoft C runtime startup code interprets command-line arguments to create the argv and argc parameters."
+ms.date: 11/09/2020
+helpviewer_keywords: ["quotation marks, command-line arguments", "double quotation marks", "double quote marks", "command line, parsing", "parsing, command-line arguments", "startup code, parsing command-line arguments"]
 ms.assetid: ffce8037-2811-45c4-8db4-1ed787859c80
 ---
 # Parsing C Command-Line Arguments
@@ -12,15 +13,17 @@ Microsoft C startup code uses the following rules when interpreting arguments gi
 
 - Arguments are delimited by white space, which is either a space or a tab.
 
-- A string surrounded by double quotation marks is interpreted as a single argument, regardless of white space contained within. A quoted string can be embedded in an argument. Note that the caret (**^**) is not recognized as an escape character or delimiter.
+- The first argument (`argv[0]`) is treated specially. It represents the program name. Because it must be a valid pathname, parts surrounded by double quote marks (**`"`**) are allowed. The double quote marks aren't included in the `argv[0]` output. The parts surrounded by double quote marks prevent interpretation of a space or tab character as the end of the argument. The later rules in this list don't apply.
 
-- A double quotation mark preceded by a backslash, **\\"**, is interpreted as a literal double quotation mark (**"**).
+- A string surrounded by double quote marks is interpreted as a single argument, whether or not it contains white space. A quoted string can be embedded in an argument. The caret (**`^`**) isn't recognized as an escape character or delimiter. Within a quoted string, a pair of double quote marks is interpreted as a single escaped double quote mark. If the command line ends before a closing double quote mark is found, then all the characters read so far are output as the last argument.
 
-- Backslashes are interpreted literally, unless they immediately precede a double quotation mark.
+- A double quote mark preceded by a backslash (**`\"`**) is interpreted as a literal double quote mark (**`"`**).
 
-- If an even number of backslashes is followed by a double quotation mark, then one backslash (**\\**) is placed in the `argv` array for every pair of backslashes (**\\\\**), and the double quotation mark (**"**) is interpreted as a string delimiter.
+- Backslashes are interpreted literally, unless they immediately precede a double quote mark.
 
-- If an odd number of backslashes is followed by a double quotation mark, then one backslash (**\\**) is placed in the `argv` array for every pair of backslashes (**\\\\**) and the double quotation mark is interpreted as an escape sequence by the remaining backslash, causing a literal double quotation mark (**"**) to be placed in `argv`.
+- If an even number of backslashes is followed by a double quote mark, then one backslash (**`\`**) is placed in the `argv` array for every pair of backslashes (**`\\`**), and the double quote mark (**`"`**) is interpreted as a string delimiter.
+
+- If an odd number of backslashes is followed by a double quote mark, then one backslash (**`\`**) is placed in the `argv` array for every pair of backslashes (**`\\`**). The double quote mark is interpreted as an escape sequence by the remaining backslash, causing a literal double quote mark (**`"`**) to be placed in `argv`.
 
 This list illustrates the rules above by showing the interpreted result passed to `argv` for several examples of command-line arguments. The output listed in the second, third, and fourth columns is from the ARGS.C program that follows the list.
 
@@ -31,13 +34,13 @@ This list illustrates the rules above by showing the interpreted result passed t
 |`a\\\b d"e f"g h`|`a\\\b`|`de fg`|`h`|
 |`a\\\"b c d`|`a\"b`|`c`|`d`|
 |`a\\\\"b c" d e`|`a\\b c`|`d`|`e`|
+|`a"b"" c d`|`ab" c d`|||
 
 ## Example
 
 ### Code
 
 ```c
-// Parsing_C_Commandline_args.c
 // ARGS.C illustrates the following variables used for accessing
 // command-line arguments and environment variables:
 // argc  argv  envp