Error Handling Return Values
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as expected is a good start. Making your programs behave properly when encountering unexpected conditions is where it really gets challenging. ¶ The problematic situations that a program can encounter fall into two categories: c error function Programmer mistakes and genuine problems. If someone forgets to pass a required argument to c error handling best practices a function, that is an example of the first kind of problem. On the other hand, if a program asks the user error handling in c++ to enter a name and it gets back an empty string, that is something the programmer can not prevent. ¶ In general, one deals with programmer errors by finding and fixing them, and with genuine
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errors by having the code check for them and perform some suitable action to remedy them (for example, asking for the name again), or at least fail in a well-defined and clean way. ¶ It is important to decide into which of these categories a certain problem falls. For example, consider our old power function:function power(base, exponent) { var result = 1; for (var count = 0; count < exponent; count++) result c error codes *= base; return result; } ¶ When some geek tries to call power("Rabbit", 4), that is quite obviously a programmer error, but how about power(9, 0.5)? The function can not handle fractional exponents, but, mathematically speaking, raising a number to the halfth power is perfectly reasonable (Math.pow can handle it). In situations where it is not entirely clear what kind of input a function accepts, it is often a good idea to explicitly state the kind of arguments that are acceptable in a comment. ¶ If a function encounters a problem that it can not solve itself, what should it do? In chapter 4 we wrote the function between:function between(string, start, end) { var startAt = string.indexOf(start) + start.length; var endAt = string.indexOf(end, startAt); return string.slice(startAt, endAt); } ¶ If the given start and end do not occur in the string, indexOf will return -1 and this version of between will return a lot of nonsense: between("Your mother!", "{-", "-}") returns "our mother". ¶ When the program is running, and the function is called like that, the code that called it will get a string value, as it expected, and happily continue doing something with it. But the value is wrong, so whatever it ends up doing with it will also be wrong. A
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What is the best way to return an error from a function when I'm already returning a value? up vote 12 down vote favorite 6 I wrote a function in C that converts a string to an integer and returns the http://eloquentjavascript.net/1st_edition/chapter5.html integer. When I call the function I also want it to let me know if the string is not a valid number. In the past I returned -1 when this error occurred, because I didn't need to convert strings to negative numbers. But now I want it to convert strings to negative numbers, so what is the best way to report the error? In case I wasn't clear about this: I don't want this function to report the error to the user, I want http://stackoverflow.com/questions/291828/what-is-the-best-way-to-return-an-error-from-a-function-when-im-already-returni it to report the error to the code that called the function. ("Report" might be the wrong word to use...) Here's the code: s32 intval(const char *string) { bool negative = false; u32 current_char = 0; if (string[0] == '-') { negative = true; current_char = 1; } s32 num = 0; while (string[current_char]) { if (string[current_char] < '0' || string[current_char] > '9') { // Return an error here.. but how? } num *= 10; num += string[current_char] - '0'; current_char++; } if (negative) { num = -num; } return num; } c return share|improve this question asked Nov 15 '08 at 0:04 Jeremy Ruten 93.6k26134172 Heh. No multiple-value-bind in C :) –Svante Nov 15 '08 at 0:44 add a comment| 7 Answers 7 active oldest votes up vote 21 down vote There are several ways. All have their pluses and minuses. Have the function return an error code and pass in a pointer to a location to return the result. The nice thing about this there's no overloading of the result. The bad thing is that you can't use the real result of the function directly in an expression. Evan Teran suggested a variation of this that has the caller pass a pointer to a success variable (which can be optionally NULL if the caller doesn't care) and returns the actual value from the function. This has the advantage of allowing the function to be used directly in expressions when the caller is OK with a de
C - Basic Syntax C - Data Types C - Variables C - Constants C - Storage Classes C - Operators C - Decision Making C - Loops C - Functions C - Scope Rules C - Arrays C - Pointers C - https://www.tutorialspoint.com/cprogramming/c_error_handling.htm Strings C - Structures C - Unions C - Bit Fields C - Typedef C - Input & Output C - File I/O C - Preprocessors C - Header Files C - Type Casting C - Error Handling C - https://codeutopia.net/blog/2010/03/11/should-a-failed-function-return-a-value-or-throw-an-exception/ Recursion C - Variable Arguments C - Memory Management C - Command Line Arguments C Programming Resources C - Questions & Answers C - Quick Guide C - Useful Resources C - Discussion Selected Reading Developer's Best Practices Questions and error handling Answers Effective Resume Writing HR Interview Questions Computer Glossary Who is Who C - Error Handling Advertisements Previous Page Next Page As such, C programming does not provide direct support for error handling but being a system programming language, it provides you access at lower level in the form of return values. Most of the C or even Unix function calls return -1 or NULL in case of any error and set an error code errno. It is set as error handling in a global variable and indicates an error occurred during any function call. You can find various error codes defined in
something: The failure case. What should a function do when it fails? There are two schools for this - the "throw an exception" school and the "return an error value" school. But which of these is the correct approach? Some background Back in ye olden times there were no exceptions. Languages like C are still being used today. In such languages the choice is quite easy to make. However, what about languages that do support exceptions? Should you strive to use the language's features to their fullest, and always throw an exception? Are error returns just relics? If you listen to people talk about this, it often turns into a debate about what they like. If you grew up with languages that had no exceptions, chances are you still prefer return codes. Similarly, if you used a lot of Java or other exceptional language, you might end up disliking return codes. However - both of them deserve merit and have their uses. Basics As you may have heard, exceptions are for exceptional conditions. But what is an exceptional condition? What isn't? Let's take an example: Your application attempts to load a resource file - for example the configuration settings for your database - and it's missing. Is this an exceptional condition? Maybe. It depends on one thing: Is it normal for it to be missing, or should the file always be there? function loadConfiguration() { var file = open('configuration.ini') if(exists(file)) { read(file) } else { throw "Configuration file is missing" } } So this pseudo-code could be a simplified configuration loading function. In this case the configuration file has to exist - let's say it's some internal file. But what if the file is something that contains settings the user has selected? In that case it might be perfectly fine for the file to not exist. The user may not have added any custom settings and as such, it's normal for the file to be missing. In this case our function could look like this: function tryLoadConfiguration() { var file = open('configuration.ini') if(e