my goal is change a function to a format where the return value of the function is treated :
For example ; treating a the function scanf()
Return value of scanf : The value EOF is returned if the end of input is reached before
either the first successful conversion or a matching failure occurs.
EOF is also returned if a read error occurs, in which case the error
indicator for the stream (see ferror(3)) is set, and errno is set to
indicate the error.
Thus
scanf("%d\n",&i);
will be change to
#define RVAL(exp) do {if ((exp) == -1) { perror (#exp); exit(1); }} while (0)
...
RVAL(scanf("%d\n",&i));
Thus I want this to be done quickly means :
so what i do is look for occurences of "scanf" and replace it with "RVAL(scanf"
but the problem is i have to add another right parentheses
Can this be done fast ? using a techniques ? or a style ? where each whenever I enter scanf(); its replaced witch rval(scanf());
If you don't have many ) in your format string you can use a regex with (scanf([^)]*)); and replace with rval(\1);
*see comment
Related
A program that loads and processes command-line arguments should be created.
Here comes a few examples on how it should look when you run it (bold text is the text that the user will type):
Terminal prompt % **./my_program**
No arguments given.
Terminal prompt % **./my_program 123**
Wrong amounts of arguments given.
Terminal prompt % **./my_program 10 XYZ 999 Greetings!**
Wrong amounts of arguments given.
Terminal prompt % **./my_program 3 HELLO**
Message: HELLOHELLOHELLO
The program "./my program" is ending.
Terminal prompt % **./my_program 0 Bye**
Message:
The program "./my program" is ending.
This is my code so far:
with Ada.Text_IO; use Ada.text_IO;
with Ada.Integer_Text_IO; use Ada.Integer_Text_IO;
with Ada.Command_Line; use Ada.Command_Line;
procedure my_program is
type String is array (Positive) of Character;
N : Integer;
Text : String;
begin
N := Argument_Count;
if N = 0 then
Put_Line("No arguments given.");
elsif N /= 2 then
Put_Line("Wrong number of arguments given.");
elsif N = 2 then
Put("Message: ");
for I in 1 .. N loop
Put(Text);
New_Line;
end loop;
Put("The program """);
Put(""" is ending. ");
end if;
end my_program;
My program handles the first 3 three cases but when I go ahead with the 4th and 5th (last) case I get an error code at the row Put(Text) where it says
Missing argument for parameter "Item" in call to "Put"
I don't know if I declared my string right because I don't want a string of a specific length. Can anyone come up with something that could help me solve case 4 and 5? It would be nice and highly appreciated
This seems to be a homework or exam question, so I would usually not provide a full answer. But Chris already gave that (with some defects), so here is my suggestion. Compared to Chris's solution, I try to avoid using unnecessary variables, and I favour case statements over if-then-else cascades, and I try to reduce the scope of exception handlers. I prefer to put use clauses in the subprogram so that the context-clause section contains only with clauses. I use the string-multiplying "*" operator from Ada.Strings.Fixed, but that is perhaps an unnecessary refinement.
with Ada.Command_Line;
with Ada.Strings.Fixed;
with Ada.Text_IO;
procedure My_Program
is
use Ada.Strings.Fixed;
use Ada.Text_IO;
begin
case Ada.Command_Line.Argument_Count is
when 0 =>
Put_Line ("No arguments given.");
when 2 =>
begin
Put_Line (
Natural'Value (Ada.Command_Line.Argument(1))
* Ada.Command_Line.Argument(2));
exception
when Constraint_Error =>
Put_Line ("Invalid input for argument 1.");
end;
when others =>
Put_Line ("Wrong amount of arguments given.");
end case;
Put_Line (
"The program """
& Ada.Command_Line.Command_Name
& """ is ending.");
end My_Program;
Note that my version:
Rejects negative first arguments (like "-3").
Outputs the repeated strings on a single line, as was required by the examples given.
Includes the name of the program in the final message, as was also required.
Given the clarification in comments as to the purpose of the program, to print a message n times where n is the first argument, and the message is the second argument, you need to parse the first argument as an integer. This can be done with Integer'Value.
Now, that raises the prospect of the user not running the program with an integer. So we have to handle the possible Constraint_Error exception.
with Ada.Text_IO; use Ada.text_IO;
with Ada.Integer_Text_IO; use Ada.Integer_Text_IO;
with Ada.Command_Line; use Ada.Command_Line;
procedure my_program is
argc : Integer;
N : Integer;
begin
argc := Argument_Count;
if argc = 0 then
Put_Line("No arguments given.");
elsif argc /= 2 then
Put_Line("Wrong number of arguments given.");
else
n := Integer'Value(Argument(1));
Put("Message: ");
for I in 1 .. N loop
Put_Line(Argument(2));
end loop;
Put("The program """);
Put(""" is ending. ");
end if;
exception
when Constraint_Error =>
Put_Line("Invalid input for argument 1.");
end my_program;
As an aside, when we've checked in our conditional if argc is zero, and that it doesn't equal two, we don't have to use elsif. The only other possibility is that it is 2.
You say
My program handles the first 3 three cases but when I go ahead with the 4th and 5th (last) case I get an error code at the row Put(Text) where it says "Missing argument for parameter "Item" in call to "Put". "
which doesn't make sense, because your program as shown doesn't compile. I guess what you mean is "when I try to add the code to handle cases 4 and 5, it doesn't compile".
The reason why it doesn’t compile is hidden in the actual error messages:
leun.adb:24:10: no candidate interpretations match the actuals:
leun.adb:24:10: missing argument for parameter "Item" in call to "put" declared at a-tiinio.ads:97, instance at a-inteio.ads:18
...
leun.adb:24:14: expected type "Standard.Integer"
leun.adb:24:14: found type "String" defined at line 7
leun.adb:24:14: ==> in call to "Put" at a-tiinio.ads:80, instance at a-inteio.
You have at line 7
type String is array (Positive) of Character;
which is both misleading and not what you meant.
It’s ’not what you meant’ because array (Positive) means an array of fixed length from 1 to Positive’Last, which will not fit into your computer’s memory. What you meant is array (Positive range <>).
Even with this correction, it's 'misleading' because although it would be textually the same as the declaration of the standard String in ARM 3.6.3(4), in Ada two different type declarations declare two different types. So, when you write Put(Text); the Put that you meant to call (the second in ARM A.10.7(16)) doesn’t match because it’s expecting a parameter of type Standard.String but Text is of type my_program.String.
Cure for this problem: don’t declare your own String type.
I have a mex function that takes in a field of a struct in the third input (i.e. prhs[2]), which is a boolean. If true, it will parse information from the fourth input (i.e. prhs[3]). In a nutshell, this is the code excerpt:
mxValue = mxGetField(prhs[3], 0, "change"); mxLogical *change;
change = mxGetLogicals(mxValue);
mexPrintf("true/false: %i \n", *change);
mexEvalString("drawnow;");
if ( change ) {
mexPrintf("...Parsing info... \n");
mexEvalString("drawnow;");
mxValue = mxGetField(prhs[3], 0, "info");
nRows = mxGetM(mxValue); nCols = mxGetN(mxValue);
Eigen::Map<Eigen::VectorXd> info((double *)mxGetPr(mxValue),nRows);
}
As you can see, I do a printout to see whether the input prhs[2] is true or false. Even if the function prints out false, the if statement gets executed regardless, because I can see the printout ...Parsing info....
Why is my MATLAB mex function ignoring my if statement?
C is not MATLAB! C is C!
You are checking if pointer change has a value. It does indeed have a value, a memory direction e.g. #72BA21, to the location where the value of the boolean is stored.
You can either check the contents of whats inside that specific direction if(*change) as #buzjwa suggest, or grab the information on the array, instead of a pointer to it, using mxGetData.
As a side note: learn to debug, or at least, print statements. a simple mexPrintf() call would have shown you what change contains
I'm new to programming and writing my first function for MATLAB. The name of the function should be "picalc".
The purpose is to accept an "x" and "y" value as input arguments. These values must be plugged into x^2+y^2, and if this result is less than or equal to 1, return true. Otherwise, return false.
Here is what I have so far:
function[true,false]=picalc(x,y);
if x^2+y^2<=1
return true
else
return false
end
Can anyone tell me why this won't work? As it stands, I get the following error:
Error: File: picalc.m Line: 6 Column: 13
Unexpected MATLAB expression.
Thank you very much for your expertise!
In MATLAB, return does not return value as an output of a function call but rather returns control to the invoking function (see documentation here). As such, it does not take argument, because what it does is merely redirecting the flow of the program to the function/statement that invokes the function/statement containing the return statement.
Your function should be written like this:
function result = picalc(x,y);
if x^2+y^2<=1
result = true;
else
result = false;
end
The variable on left hand side of the function declaration is the output variable. By assigning value to this valuable, you are "returning" an output.
I'm a progress noob, actually having problem with basic blocks.
Below the issue is in my if else statement. It works fine when its just if, then, else then, but when I want to put in more than one statement into the if portion, I have to put it in a block, so I'm using if, then do: else, then do: but these aren't working for me. Any obvious errors you can see? My error message is **Colon followed by white space terminates a statement. (199)
INPUT FROM "r:\_content\stephen\4gl apps\dpl\output.csv".
REPEAT:
ASSIGN i_cntr = (i_cntr + 1).
myRow = "".
IMPORT DELIMITER ',' myRow.
IF myRow[5] <> "" THEN DO:
/*change this to assign 2 rows - 2 creates - 2 sets of four*/
c_fname = myRow[1].
MESSAGE
c_fname SKIP
myRow[2] SKIP
myRow[3] skip
myRow[4] skip
myRow[5] SKIP
i_cntr
VIEW-AS ALERT-BOX INFO BUTTONS OK.
END./*end of if, then do:*/
ELSE IF myRow[5] = "" THEN DO:
MESSAGE
myRow[1] SKIP
myRow[2] skip
myRow[3] skip
myRow[4] skip
i_cntr
VIEW-AS ALERT-BOX INFO BUTTONS OK.
END./*end of else if, then do:*/
END./*end of repeat*/
A very simple syntax error: you need at least one space after the END-statement.
END. /*end of if, then do:*/
/* ^ Make sure there's space above here! */
And if you don't want to follow the excellent advice in Tims answer (use CASE). This is the "complete" syntax of the IF statement.
IF expression1 THEN DO:
/* Code goes here */
END.
ELSE IF expression2 THEN DO:
/* Code goes here */
END.
ELSE DO:
/* Code goes here */
END.
expressions:
A constant, field name, variable name, or expression whose value is logical (TRUE or FALSE). The expression can include comparisons, logical operators, and parentheses.
You can also leave out the DO: END. When the IF code to be executed only consists of a single statement:
IF TRUE THEN DISPLAY "TRUE".
ELSE DISPLAY "NOT TRUE".
You could also use other block-statements (such as FOR or REPEAT) but that will most likely only create code that is hard to read.
Rather than using nested IF/ELSE, you'd be better off using a CASE statement like so:
CASE varname:
WHEN "" THEN DO: /*something */ END.
WHEN "value" THEN DO: /*something */ END.
OTHERWISE DO: /*something */ END.
END CASE.
Check the docs on this statement for more details.
I figured out the issue. This wasn't caused by a coding error. Apparently Progress doesn't like comments too close to the code, which caused it to throw an error.
END. /*end of if, then do:*/ => This is ok.
END./*end of if, then do:*/ => This caused the issue comments too close to statement.
Thanks To Tim Kuehn for his response.
In most OO languages, where variables may point to objects, they may also have a null value, which is highly convenient.
In Matlab, I have a function which parses a command, and then returns a cell array, or false (which is equal to zero — which is another common pattern) if it fails:
function re = parse(s)
...
if (invalid)
re = false;
return;
end
end
The problem is that when I check the result, it gives an error:
re = parse(s);
if (false == re)
Undefined function 'eq' for input arguments of type 'cell'.
I've written a function to check it without an error: strcmp('logical', class(re)) && false == re, but that seems to be really slow for use in hot areas of the code, and also inconvenient if I have to add this function to every M file I'm writing.
Using NaN is even worse, because besides throwing that error, it also isn't equal to itself.
What's a better alternative for use with this pattern?
You can use the isequal function to compare any two items without causing that error. For example:
if isequal (re, false)
%code here
end
A good alternative is to use the empty array: [] and isempty(re) to check. This doesn't throw the error.
Reference: http://www.mathworks.com.au/matlabcentral/newsreader/view_thread/148764
If you can change the function parse one solution would be to return two output arguments [re status] = parse(s), where status would be logical variable. Set it to true in case of success, and to false otherwise.
I would use the empty cell array {} if it is not a valid result otherwise. Using empty matrices is MATLAB standard (see Evgeni Sergeev's answer), but using an empty cell array instead of an empty numeric array ensures that you'll always end up with the same type of result.
If, on the other hand, the empty cell array {} is a valid result of your function, then I'd use an exception to signalize a problem:
if invalid
error('Parse:InvalidArgumentError', 'The input is invalid.');
end
Make sure to use an appropriate error ID (first argument to error) so that you can catch exactly that exception when you call the function:
try:
result = parse(something);
catch ME
if strcmp(ME.identifier, 'Parse:InvalidArgumentError')
fprintf('Ooops\n');
else
% Some other error
ME.rethrow();
end
end
I think the problem is that matlab functions don't return pointers but copies of values.
IMHO the best best approach would be to define your own "pointer" class. Inside you can define an "isNull()" command or even override comparison to produce the behavior you desire.