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Tcl_ParseCommand(3) Tcl Library Procedures Tcl_ParseCommand(3) ______________________________________________________________________________ NAME Tcl_ParseCommand, Tcl_ParseExpr, Tcl_ParseBraces, Tcl_ParseQuoted- String, Tcl_ParseVarName, Tcl_ParseVar, Tcl_FreeParse, Tcl_EvalTokens- Standard - parse Tcl scripts and expressions SYNOPSIS #include <tcl.h> int Tcl_ParseCommand(interp, start, numBytes, nested, parsePtr) int Tcl_ParseExpr(interp, start, numBytes, parsePtr) int Tcl_ParseBraces(interp, start, numBytes, parsePtr, append, termPtr) int Tcl_ParseQuotedString(interp, start, numBytes, parsePtr, append, termPtr) int Tcl_ParseVarName(interp, start, numBytes, parsePtr, append) const char * Tcl_ParseVar(interp, start, termPtr) Tcl_FreeParse(usedParsePtr) int Tcl_EvalTokensStandard(interp, tokenPtr, numTokens) ARGUMENTS Tcl_Interp *interp (out) For procedures other than Tcl_FreeParse and Tcl_EvalTo- kensStandard, used only for er- ror reporting; if NULL, then no error messages are left after errors. For Tcl_EvalTokensStan- dard, determines the context for evaluating the script and also is used for error reporting; must not be NULL. const char *start (in) Pointer to first character in string to parse. Tcl_Size numBytes (in) Number of bytes in string to parse, not including any termi- nating null character. If less than 0 then the script consists of all characters following start up to the first null char- acter. int nested (in) Non-zero means that the script is part of a command substitu- tion so an unquoted close bracket should be treated as a command terminator. If zero, close brackets have no special meaning. int append (in) Non-zero means that *parsePtr already contains valid tokens; the new tokens should be ap- pended to those already present. Zero means that *parsePtr is uninitialized; any information in it is ignored. This argument is normally 0. Tcl_Parse *parsePtr (out) Points to structure to fill in with information about the parsed command, expression, variable name, etc. Any previ- ous information in this struc- ture is ignored, unless append is non-zero in a call to Tcl_ParseBraces, Tcl_ParseQuot- edString, or Tcl_ParseVarName. const char **termPtr (out) If not NULL, points to a loca- tion where Tcl_ParseBraces, Tcl_ParseQuotedString, and Tcl_ParseVar will store a pointer to the character just after the terminating character (the close-brace, the last char- acter of the variable name, or the close-quote (respectively)) if the parse was successful. Tcl_Parse *usedParsePtr (in) Points to structure that was filled in by a previous call to Tcl_ParseCommand, Tcl_ParseExpr, Tcl_ParseVarName, etc. ______________________________________________________________________________ DESCRIPTION These procedures parse Tcl commands or portions of Tcl commands such as expressions or references to variables. Each procedure takes a pointer to a script (or portion thereof) and fills in the structure pointed to by parsePtr with a collection of tokens describing the information that was parsed. The procedures normally return TCL_OK. However, if an er- ror occurs then they return TCL_ERROR, leave an error message in in- terp's result (if interp is not NULL), and leave nothing in parsePtr. Tcl_ParseCommand is a procedure that parses Tcl scripts. Given a pointer to a script, it parses the first command from the script. If the command was parsed successfully, Tcl_ParseCommand returns TCL_OK and fills in the structure pointed to by parsePtr with information about the structure of the command (see below for details). If an er- ror occurred in parsing the command then TCL_ERROR is returned, an er- ror message is left in interp's result, and no information is left at *parsePtr. Tcl_ParseExpr parses Tcl expressions. Given a pointer to a script con- taining an expression, Tcl_ParseExpr parses the expression. If the ex- pression was parsed successfully, Tcl_ParseExpr returns TCL_OK and fills in the structure pointed to by parsePtr with information about the structure of the expression (see below for details). If an error occurred in parsing the command then TCL_ERROR is returned, an error message is left in interp's result, and no information is left at *parsePtr. Tcl_ParseBraces parses a string or command argument enclosed in braces such as {hello} or {string \t with \t tabs} from the beginning of its argument start. The first character of start must be {. If the braced string was parsed successfully, Tcl_ParseBraces returns TCL_OK, fills in the structure pointed to by parsePtr with information about the structure of the string (see below for details), and stores a pointer to the character just after the terminating } in the location given by *termPtr. If an error occurs while parsing the string then TCL_ERROR is returned, an error message is left in interp's result, and no infor- mation is left at *parsePtr or *termPtr. Tcl_ParseQuotedString parses a double-quoted string such as "sum is [expr {$a+$b}]" from the beginning of the argument start. The first character of start must be ". If the double-quoted string was parsed successfully, Tcl_ParseQuotedString returns TCL_OK, fills in the struc- ture pointed to by parsePtr with information about the structure of the string (see below for details), and stores a pointer to the character just after the terminating " in the location given by *termPtr. If an error occurs while parsing the string then TCL_ERROR is returned, an error message is left in interp's result, and no information is left at *parsePtr or *termPtr. Tcl_ParseVarName parses a Tcl variable reference such as $abc or $x([expr {$index + 1}]) from the beginning of its start argument. The first character of start must be $. If a variable name was parsed suc- cessfully, Tcl_ParseVarName returns TCL_OK and fills in the structure pointed to by parsePtr with information about the structure of the variable name (see below for details). If an error occurs while pars- ing the command then TCL_ERROR is returned, an error message is left in interp's result (if interp is not NULL), and no information is left at *parsePtr. Tcl_ParseVar parses a Tcl variable reference such as $abc or $x([expr {$index + 1}]) from the beginning of its start argument. The first character of start must be $. If the variable name is parsed success- fully, Tcl_ParseVar returns a pointer to the string value of the vari- able. If an error occurs while parsing, then NULL is returned and an error message is left in interp's result. The information left at *parsePtr by Tcl_ParseCommand, Tcl_ParseExpr, Tcl_ParseBraces, Tcl_ParseQuotedString, and Tcl_ParseVarName may in- clude dynamically allocated memory. If these five parsing procedures return TCL_OK then the caller must invoke Tcl_FreeParse to release the storage at *parsePtr. These procedures ignore any existing information in *parsePtr (unless append is non-zero), so if repeated calls are be- ing made to any of them then Tcl_FreeParse must be invoked once after each call. Tcl_EvalTokensStandard evaluates a sequence of parse tokens from a Tcl_Parse structure. The tokens typically consist of all the tokens in a word or all the tokens that make up the index for a reference to an array variable. Tcl_EvalTokensStandard performs the substitutions re- quested by the tokens and concatenates the resulting values. The re- turn value from Tcl_EvalTokensStandard is a Tcl completion code with one of the values TCL_OK, TCL_ERROR, TCL_RETURN, TCL_BREAK, or TCL_CON- TINUE, or possibly some other integer value originating in an exten- sion. In addition, a result value or error message is left in interp's result; it can be retrieved using Tcl_GetObjResult. TCL_PARSE STRUCTURE Tcl_ParseCommand, Tcl_ParseExpr, Tcl_ParseBraces, Tcl_ParseQuoted- String, and Tcl_ParseVarName return parse information in two data structures, Tcl_Parse and Tcl_Token: typedef struct { const char *commentStart; Tcl_Size commentSize; const char *commandStart; Tcl_Size commandSize; Tcl_Size numWords; Tcl_Token *tokenPtr; Tcl_Size numTokens; ... } Tcl_Parse; typedef struct { int type; const char *start; Tcl_Size size; Tcl_Size numComponents; } Tcl_Token; The first five fields of a Tcl_Parse structure are filled in only by Tcl_ParseCommand. These fields are not used by the other parsing pro- cedures. Tcl_ParseCommand fills in a Tcl_Parse structure with information that describes one Tcl command and any comments that precede the command. If there are comments, the commentStart field points to the # character that begins the first comment and commentSize indicates the number of bytes in all of the comments preceding the command, including the new- line character that terminates the last comment. If the command is not preceded by any comments, commentSize is 0. Tcl_ParseCommand also sets the commandStart field to point to the first character of the first word in the command (skipping any comments and leading space) and com- mandSize gives the total number of bytes in the command, including the character pointed to by commandStart up to and including the newline, close bracket, or semicolon character that terminates the command. The numWords field gives the total number of words in the command. All parsing procedures set the remaining fields, tokenPtr and numTo- kens. The tokenPtr field points to the first in an array of Tcl_Token structures that describe the components of the entity being parsed. The numTokens field gives the total number of tokens present in the ar- ray. Each token contains four fields. The type field selects one of several token types that are described below. The start field points to the first character in the token and the size field gives the total number of characters in the token. Some token types, such as TCL_TO- KEN_WORD and TCL_TOKEN_VARIABLE, consist of several component tokens, which immediately follow the parent token; the numComponents field de- scribes how many of these there are. The type field has one of the following values: TCL_TOKEN_WORD This token ordinarily describes one word of a command but it may also describe a quoted or braced string in an expression. The token describes a component of the script that is the result of concatenating together a sequence of subcomponents, each de- scribed by a separate subtoken. The token starts with the first non-blank character of the component (which may be a double- quote or open brace) and includes all characters in the compo- nent up to but not including the space, semicolon, close bracket, close quote, or close brace that terminates the compo- nent. The numComponents field counts the total number of sub- tokens that make up the word, including sub-tokens of TCL_TO- KEN_VARIABLE and TCL_TOKEN_BS tokens. TCL_TOKEN_SIMPLE_WORD This token has the same meaning as TCL_TOKEN_WORD, except that the word is guaranteed to consist of a single TCL_TOKEN_TEXT sub-token. The numComponents field is always 1. TCL_TOKEN_EXPAND_WORD This token has the same meaning as TCL_TOKEN_WORD, except that the command parser notes this word began with the expansion pre- fix {*}, indicating that after substitution, the list value of this word should be expanded to form multiple arguments in com- mand evaluation. This token type can only be created by Tcl_ParseCommand. TCL_TOKEN_TEXT The token describes a range of literal text that is part of a word. The numComponents field is always 0. TCL_TOKEN_BS The token describes a backslash sequence such as \n or \0xA3. The numComponents field is always 0. TCL_TOKEN_COMMAND The token describes a command whose result must be substituted into the word. The token includes the square brackets that sur- round the command. The numComponents field is always 0 (the nested command is not parsed; call Tcl_ParseCommand recursively if you want to see its tokens). TCL_TOKEN_VARIABLE The token describes a variable substitution, including the $, variable name, and array index (if there is one) up through the close parenthesis that terminates the index. This token is fol- lowed by one or more additional tokens that describe the vari- able name and array index. If numComponents is 1 then the variable is a scalar and the next token is a TCL_TOKEN_TEXT to- ken that gives the variable name. If numComponents is greater than 1 then the variable is an array: the first sub-token is a TCL_TOKEN_TEXT token giving the array name and the remaining sub-tokens are TCL_TOKEN_TEXT, TCL_TOKEN_BS, TCL_TOKEN_COMMAND, and TCL_TOKEN_VARIABLE tokens that must be concatenated to pro- duce the array index. The numComponents field includes nested sub-tokens that are part of TCL_TOKEN_VARIABLE tokens in the ar- ray index. TCL_TOKEN_SUB_EXPR The token describes one subexpression of an expression (or an entire expression). A subexpression may consist of a value such as an integer literal, variable substitution, or parenthesized subexpression; it may also consist of an operator and its operands. The token starts with the first non-blank character of the subexpression up to but not including the space, brace, close-paren, or bracket that terminates the subexpression. This token is followed by one or more additional tokens that describe the subexpression. If the first sub-token after the TCL_TO- KEN_SUB_EXPR token is a TCL_TOKEN_OPERATOR token, the subexpres- sion consists of an operator and its token operands. If the op- erator has no operands, the subexpression consists of just the TCL_TOKEN_OPERATOR token. Each operand is described by a TCL_TOKEN_SUB_EXPR token. Otherwise, the subexpression is a value described by one of the token types TCL_TOKEN_WORD, TCL_TOKEN_TEXT, TCL_TOKEN_BS, TCL_TOKEN_COMMAND, TCL_TOKEN_VARI- ABLE, and TCL_TOKEN_SUB_EXPR. The numComponents field counts the total number of sub-tokens that make up the subexpression; this includes the sub-tokens for any nested TCL_TOKEN_SUB_EXPR tokens. TCL_TOKEN_OPERATOR The token describes one operator of an expression such as && or hypot. A TCL_TOKEN_OPERATOR token is always preceded by a TCL_TOKEN_SUB_EXPR token that describes the operator and its operands; the TCL_TOKEN_SUB_EXPR token's numComponents field can be used to determine the number of operands. A binary operator such as * is followed by two TCL_TOKEN_SUB_EXPR tokens that de- scribe its operands. A unary operator like - is followed by a single TCL_TOKEN_SUB_EXPR token for its operand. If the opera- tor is a math function such as log10, the TCL_TOKEN_OPERATOR to- ken will give its name and the following TCL_TOKEN_SUB_EXPR to- kens will describe its operands; if there are no operands (as with rand), no TCL_TOKEN_SUB_EXPR tokens follow. There is one trinary operator, ?, that appears in if-then-else subexpressions such as x?y:z; in this case, the ? TCL_TOKEN_OPERATOR token is followed by three TCL_TOKEN_SUB_EXPR tokens for the operands x, y, and z. The numComponents field for a TCL_TOKEN_OPERATOR to- ken is always 0. After Tcl_ParseCommand returns, the first token pointed to by the to- kenPtr field of the Tcl_Parse structure always has type TCL_TOKEN_WORD or TCL_TOKEN_SIMPLE_WORD or TCL_TOKEN_EXPAND_WORD. It is followed by the sub-tokens that must be concatenated to produce the value of that word. The next token is the TCL_TOKEN_WORD or TCL_TOKEN_SIMPLE_WORD of TCL_TOKEN_EXPAND_WORD token for the second word, followed by sub-tokens for that word, and so on until all numWords have been accounted for. After Tcl_ParseExpr returns, the first token pointed to by the tokenPtr field of the Tcl_Parse structure always has type TCL_TOKEN_SUB_EXPR. It is followed by the sub-tokens that must be evaluated to produce the value of the expression. Only the token information in the Tcl_Parse structure is modified: the commentStart, commentSize, commandStart, and commandSize fields are not modified by Tcl_ParseExpr. After Tcl_ParseBraces returns, the array of tokens pointed to by the tokenPtr field of the Tcl_Parse structure will contain a single TCL_TO- KEN_TEXT token if the braced string does not contain any backslash-new- lines. If the string does contain backslash-newlines, the array of to- kens will contain one or more TCL_TOKEN_TEXT or TCL_TOKEN_BS sub-tokens that must be concatenated to produce the value of the string. If the braced string was just {} (that is, the string was empty), the single TCL_TOKEN_TEXT token will have a size field containing zero; this en- sures that at least one token appears to describe the braced string. Only the token information in the Tcl_Parse structure is modified: the commentStart, commentSize, commandStart, and commandSize fields are not modified by Tcl_ParseBraces. After Tcl_ParseQuotedString returns, the array of tokens pointed to by the tokenPtr field of the Tcl_Parse structure depends on the contents of the quoted string. It will consist of one or more TCL_TOKEN_TEXT, TCL_TOKEN_BS, TCL_TOKEN_COMMAND, and TCL_TOKEN_VARIABLE sub-tokens. The array always contains at least one token; for example, if the argu- ment start is empty, the array returned consists of a single TCL_TO- KEN_TEXT token with a zero size field. Only the token information in the Tcl_Parse structure is modified: the commentStart, commentSize, commandStart, and commandSize fields are not modified. After Tcl_ParseVarName returns, the first token pointed to by the to- kenPtr field of the Tcl_Parse structure always has type TCL_TOKEN_VARI- ABLE. It is followed by the sub-tokens that make up the variable name as described above. The total length of the variable name is contained in the size field of the first token. As in Tcl_ParseExpr, only the token information in the Tcl_Parse structure is modified by Tcl_Parse- VarName: the commentStart, commentSize, commandStart, and commandSize fields are not modified. All of the character pointers in the Tcl_Parse and Tcl_Token structures refer to characters in the start argument passed to Tcl_ParseCommand, Tcl_ParseExpr, Tcl_ParseBraces, Tcl_ParseQuotedString, and Tcl_Parse- VarName. There are additional fields in the Tcl_Parse structure after the numTo- kens field, but these are for the private use of Tcl_ParseCommand, Tcl_ParseExpr, Tcl_ParseBraces, Tcl_ParseQuotedString, and Tcl_Parse- VarName; they should not be referenced by code outside of these proce- dures. KEYWORDS backslash substitution, braces, command, expression, parse, token, variable substitution Tcl 8.3 Tcl_ParseCommand(3)
NAME | SYNOPSIS | ARGUMENTS | DESCRIPTION | TCL_PARSE STRUCTURE | KEYWORDS
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