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Text File | 1992-04-28 | 17.6 KB | 595 lines

PRODUCT : Turbo Pascal NUMBER : 994 VERSION : All OS : DOS DATE : April 28, 1992 PAGE : 1/9 TITLE : Turbo Pascal vs ANSI Pascal ================================================================= Comparing Turbo Pascal 6.0 with ANSI Pascal ================================================================= ----------------------------------------------------------------- Table of Contents ----------------------------------------------------------------- 1. Exceptions to ANSI Pascal requirements 2. Extensions to ANSI Pascal 3. Implementation-dependent features 4. Treatment of errors ----------------------------------------------------------------- This appendix compares Turbo Pascal to ANSI Pascal as defined by ANSI/IEEE770X3.97-1983 in the book American National Standard Pascal Computer Programming Language (ISBN 0-471-88944-X, published by The Institute of Electrical and Electronics Engineers in New York). =========================================== 1. Exceptions to ANSI Pascal requirements =========================================== Turbo Pascal is unable to detect whether a program violates any of the exceptions listed here. Turbo Pascal complies with the requirements of ANSI/IEEE770X3.97-1983 with the following exceptions: o In ANSI Pascal, an identifier can be of any length and all characters are significant. In Turbo Pascal, an identifier can be of any length, but only the first 63 characters are significant. o In ANSI Pascal, the @ symbol is an alternative for the ^ symbol. In Turbo Pascal, the @ symbol is an operator, which is never treated identically with the ^ symbol. PRODUCT : Turbo Pascal NUMBER : 994 VERSION : All OS : DOS DATE : April 28, 1992 PAGE : 2/9 TITLE : Turbo Pascal vs ANSI Pascal o In ANSI Pascal, a comment can begin with { and end with *), or begin with (* and end with }. In Turbo Pascal, comments must begin and end with the same set of symbols. o In ANSI Pascal, each possible value of the tag type in a variant part must appear once. In Turbo Pascal, this requirement is not enforced. o In ANSI Pascal, the component type of a file type cannot be a structured type having a component of a file type. In Turbo Pascal, this requirement is not enforced. o In ANSI Pascal, a file variable has an associated buffer variable, which is referenced by writing the ^ symbol after the file variable. In Turbo Pascal, a file variable does not have an associated buffer variable, and writing the ^ symbol after a file variable is an error. o In ANSI Pascal, the statement part of a function must contain at least one assignment to the function identifier. In Turbo Pascal, this requirement is not enforced. o In ANSI Pascal, a field that is the selector of a variant part cannot be an actual variable parameter. In Turbo Pascal, this requirement is not enforced. o In ANSI Pascal, a component of a variable of a packed type cannot be an actual variable parameter. In Turbo Pascal, this requirement is not enforced. o In ANSI Pascal, a procedural or functional parameter is declared by writing a procedure or function heading in the formal parameter list. In Turbo Pascal, the declaration of a procedural or functional parameter is achieved through a procedural or functional type, and uses the same syntax as the declaration of other types of parameters. o In ANSI Pascal, the standard procedures Reset and Rewrite do not require pre-initialization of file variables. In Turbo Pascal, file variables must be assigned the name of an external file using the Assign procedure before they are passed to Reset or Rewrite. PRODUCT : Turbo Pascal NUMBER : 994 VERSION : All OS : DOS DATE : April 28, 1992 PAGE : 3/9 TITLE : Turbo Pascal vs ANSI Pascal o ANSI Pascal defines the standard procedures Get and Put, which are used to read from and write to files. These procedures are not defined in Turbo Pascal. o In ANSI Pascal, the syntax New(p,c1,...,cn) creates a dynamic variable with a specific active variant. In Turbo Pascal, this syntax is not allowed. o In ANSI Pascal, the syntax Dispose(q,k1,...,km) removes a dynamic variable with a specific active variant. In Turbo Pascal, this syntax is not allowed. o ANSI Pascal defines the standard procedures Pack and Unpack, which are used to "pack" and "unpack" packed variables. These procedures are not defined in Turbo Pascal. o In ANSI Pascal, the term i mod j always computes a positive value, and it is an error if j is zero or negative. In Turbo Pascal, i mod j is computed as i - (i div j) * j, and it is not an error if j is negative. o In ANSI Pascal, a goto statement within a block can refer to a label in an enclosing block. In Turbo Pascal, this is an error. o In ANSI Pascal, it is an error if the value of the selector in a case statement is not equal to any of the case constants. In Turbo Pascal, this is not an error; instead, the case statement is ignored unless it contains an else clause. o In ANSI Pascal, statements that threaten the control variable of a for statement are not allowed. In Turbo Pascal, this requirement is not enforced. o In ANSI Pascal, a Read from a text file with a Char-type variable assigns a blank to the variable if Eoln was True before the Read. In Turbo Pascal, a carriage return character (ASCII 13) is assigned to the variable in this situation. o In ANSI Pascal, a Read from a text file with an integer- type or real-type variable ceases as soon as the next PRODUCT : Turbo Pascal NUMBER : 994 VERSION : All OS : DOS DATE : April 28, 1992 PAGE : 4/9 TITLE : Turbo Pascal vs ANSI Pascal character in the file is not part of a signed integer or a signed number. In Turbo Pascal, reading ceases when the next character in the file is a blank or a control character (including the end-of-line marker). o In ANSI Pascal, a Write to a text file with a packed string-type value causes the string to be truncated if the specified field width is less than the length of the string. In Turbo Pascal, the string is always written in full, even if it is longer than the specified field width. o ANSI Pascal defines the standard procedure Page, which causes all subsequent output to a specific text file to be written on a new page. This procedure is not defined in Turbo Pascal. However, the typical equivalent of Page(F) is Write(F,Chr(12)). ============================== 2. Extensions to ANSI Pascal ============================== Turbo Pascal is unable to detect whether a program uses any of the extensions listed here. The following Turbo Pascal features are extensions to Pascal as specified by ANSI/IEEE770X3.97-1983. o The following are reserved words in Turbo Pascal: absolute inline shr assembler interface string constructor interrupt unit destructor object virtual external private uses far near xor implementation shl o An identifier can contain underscore characters (_). o Integer constants can be written in hexadecimal notation; such constants are prefixed by a $. o Identifiers can serve as labels. PRODUCT : Turbo Pascal NUMBER : 994 VERSION : All OS : DOS DATE : April 28, 1992 PAGE : 5/9 TITLE : Turbo Pascal vs ANSI Pascal o String constants are compatible with the Turbo Pascal string types, and can contain control characters and other nonprintable characters. o Label, constant, type, variable, procedure, and function declarations can occur any number of times in any order in a block. o Wherever the syntax of ANSI Pascal requires a simple constant, Turbo Pascal allows the use of a constant expression (also known as a computed constant). o Turbo Pascal implements the additional integer types Shortint, Longint, Byte, and Word, and the additional real types Single, Double, Extended, and Comp. o Turbo Pascal implements string types, which differ from the packed string types defined by ANSI Pascal in that they include a dynamic-length attribute that can vary during execution. o Turbo Pascal implements procedural and functional types. In addition to procedural and functional parameters, these types make possible the declaration and use of procedural and functional variables. o The type compatibility rules are extended to make Char types and packed string types compatible with string types. o Variables can be declared at absolute memory addresses using an absolute clause. o A variable reference can contain a call to a pointer-type function, the result of which is then dereferenced to denote a dynamic variable. o String-type variables can be indexed as arrays to access individual characters in a string. o The type of a variable reference can be changed to another type through a variable typecast. PRODUCT : Turbo Pascal NUMBER : 994 VERSION : All OS : DOS DATE : April 28, 1992 PAGE : 6/9 TITLE : Turbo Pascal vs ANSI Pascal o Turbo Pascal implements typed constants, which can be used to declare initialized variables of all types except file types. o Turbo Pascal implements three new logical operators: xor, shl, and shr. o The not, and, or, and xor operators can be used with integer-type operands to perform bitwise logical operations. o The + operator can be used to concatenate strings. o The relational operators can be used to compare strings. o Turbo Pascal implements the @ operator, which is used to obtain the address of a variable or a procedure or function. o The type of an expression can be changed to another type through a value typecast. o The case statement allows constant ranges in case label lists, and provides an optional else part. o Procedures and functions can be declared with external, inline, and interrupt directives to support assembly language subroutines, inline machine code, and interrupt procedures. o A variable parameter can be untyped (typeless), in which case any variable reference can serve as the actual parameter. o Turbo Pascal implements units to facilitate modular programming and separate compilation. o Turbo Pascal implements the following file-handling procedures and functions, which are not available in ANSI Pascal: Append FilePos Rename BlockRead FileSize RmDir BlockWrite Flush Seek ChDir GetDir SeekEof PRODUCT : Turbo Pascal NUMBER : 994 VERSION : All OS : DOS DATE : April 28, 1992 PAGE : 7/9 TITLE : Turbo Pascal vs ANSI Pascal Close MkDir SeekEoln Erase o String-type values can be input and output with the Read, Readln, Write, and Writeln standard procedures. o Turbo Pascal implements the following standard procedures and functions, which are not found in ANSI Pascal: Addr Inc Ptr Concat Insert Random Copy Int Randomize CSeg Length Release DSeg Lo RunError Dec Mark SPtr Delete MaxAvail Seg Exit MemAvail SizeOf FillChar Move SSeg Frac Ofs Str FreeMem ParamCount Swap GetMem ParamStr TypeOf Halt Pi UpCase Hi Pos Val o Turbo Pascal implements further standard constants, types, variables, procedures, and functions through standard units. ====================================== 3. Implementation-dependent features ====================================== The effect of using an implementation-dependent feature of Pascal, as defined by ANSI/IEEE770X3.97-1983, is unspecified. Programs should not depend on any specific path being taken in cases where an implementation-dependent feature is being used. Implementation-dependent features include: o the order of evaluation of index expressions in a variable reference PRODUCT : Turbo Pascal NUMBER : 994 VERSION : All OS : DOS DATE : April 28, 1992 PAGE : 8/9 TITLE : Turbo Pascal vs ANSI Pascal o the order of evaluation of expressions in a set constructor o the order of evaluation of operands of a binary operator o the order of evaluation of actual parameters in a function call o the order of evaluation of the left and right sides of an assignment o the order of evaluation of actual parameters in a procedure statement o the effect of reading a text file to which the procedure Page was applied during its creation o the binding of variables denoted by the program parameters to entities external to the program ======================== 4. Treatment of errors ======================== This section lists those errors from Appendix D of the ANSI Pascal Standard that are not automatically detected by Turbo Pascal. The numbers referred to here are the numbers used in the ANSI Pascal Standard. Errors 6, 19-22, and 25-31 are not detected because they are not applicable to Turbo Pascal. 2. If t is a tag field in a variant part and f is a field within the active variant of that variant part, it is an error to alter the value of t while a reference to f exists. This error is not detected. 3. If p is a pointer variable, it is an error to reference p^ if p is nil. This error is not detected. 4. If p is a pointer variable, it is an error to reference p^ if p is undefined. This error is not detected. PRODUCT : Turbo Pascal NUMBER : 994 VERSION : All OS : DOS DATE : April 28, 1992 PAGE : 9/9 TITLE : Turbo Pascal vs ANSI Pascal 5. If p is a pointer variable, it is an error to alter the value of p while a reference to p^ exists. This error is not detected. 42. The function call Eoln(f) is an error if Eof(f) is True. In Turbo Pascal this is not an error, and Eoln(f) is True when Eof(f) is True. 43. It is an error to reference a variable in an expression if the value of that variable is undefined. This error is not detected. 46. A term of the form i mod j is an error if j is zero or negative. In Turbo Pascal, it is not an error if j is negative. 48. It is an error if a function does not assign a result value to the function identifier. This error is not detected. 51. It is an error if the value of the selector in a case statement is not equal to any of the case constants. In Turbo Pascal, this is not an error; instead, the case statement is ignored unless it contains an else clause.