And now, doing embedded, I understand there are still extremely tight environments. I created and have been maintaining an embedded C application with about , LOC for about 7 years now. So, not super big, and not super long, but certainly enough scale to have studied, experimented, and learned a few things not many. It has enough memory, it has enough speed.
So, like others who have commented, I use goto for exception handling, with a very limited allowed construct. I allow one labeled exit point as the target for goto. One or more goto instances are allowed, but each must always go forward to the one same labeled point, and they must being going forward for the same reason. For me, the classic example is input validation. Some have very rare, but useful purposes. Inexperienced programmers write difficult to manage code regardless of goto.
Education and experience is the key to all good code, and to appropriate use of all programming language capabilities. IMO, change the discussion to where does goto add real value which of course depends on what you consider valuable , and start teaching newbies to restrict its use to those areas — just like you would teach newbies the appropriate places to use subclassing and patterns.
Compare to multiple return points where you need to remember which resources to free at each return point. With the goto method, the amount of code which is exercised in a given error condition is minimised. Most code is common to error and Ok conditions. Alternatively stated, when something occurs that influences nominal code path execution, real problems, far outside the severity of the initial issue, may result.
Use of goto as an exception handler allows code design to minimize new code execution as the result of an atypical condition and therefore reduce the possibility of ancillary issues in the newly executed code.
This increases code quality. The goto statement, therefore, should be permitted for use as an exception handler. Consider code to read a file into memory, process the data, and return some calculated value. Along the way, malloc must be used. Of course, free and CloseFile must always be executed; regardless of any error handling. At most, the return value is set. There is not a lot of code to introduce errors. More specifically, code path execution of any exceptional case is highly similar to the nominal case.
Errors in nominal code execution will more likely be caught during development. No matter what happens free and CloseFile are always executed. These were omitted in the above for brevity, but their presence does not change any of the above points about the use of goto as a means of code quality improvement.
Agree with Greg and Tom — only use I envision of goto in C is for specifically cleaning up on error, freeing stray memory and returning with an error code. That is an interesting approach, Jim. Goto is very useful in exception handling within nested blocks. In this case pragmatism beats purity: Goto should be narrowly allowed. So what can be done: 1 limit the allowed uses of the goto — this has already been done. Same module, label must be below the goto. To enforce use of this, a goto should only work to a label that lists its name in a comefrom clause.
The benefit of this should be clear that when you see a label you will know all the goto s that are allowed to jump to it. Paddock above. Code reviews can aid groups with enforcing good goto usage.
Thankfully, bad goto usage is easy to spot. As we can see from the contributions above a good case can be made on each side of the use of GOTO.
For what it is worth, I would support the use of GOTO for exception handling and enabling a single exit point from a function. Having said that, the use of GOTO should be strongly challenged at code review. Having to add flags and enclosing if statements obfuscates the actual intent of the code and can be just as buggy when a later maintenance operation has to figure out all of the conditions that allow a section of code to execute.
When there is a discontinuity between two points, for example a square wave, what are the frequency components which make up this signal? They would be in harmonics of the frequency of the square wave which stretch to infinity ideally.
Similarly, in a goto statement, we can talk about sequentiality of the code, and the bandwidth is our mind, our mind is capable of dealing with linear sequences and breaks in sequentiality is when we start to lose track and get confused.
The further the break and the more it is interleaved in other sequences of code is where mistakes will be made more easily. Our mind is not dependendable all the time and not only this, the original author may not even be the same person maintaining the code in the future which is usually the case. It is even more difficult for others to keep track of discontinuous breaks in the code. My internal coding standard which I wrote over 25 years ago, and which bears a strong resemblance to yours bans goto.
Arguments about linux kernel and exceptions are I think a different case not generally relevant to bug-busting in embedded systems. I have not had or felt the need for using goto for many years writing very complex code, including many simple time based schedulers with multiple cooperating tasks.
The first time I came across goto recently was in some code I had to adapt. This code was is an exemplar of bad practice. No useful comments. No useful naming. Crazy use of type names if at all.
Pointers all over the place to obscure structures overlaid by use of unions with no sensible context. Gotos jumping all around the place. Some names exported from code units and some not. Cross-module calling all over the place without relevant header files being included. Better off starting again. Mind you — my coding standard also has a get-out clause: All rules in the standard can be broken, provided there is a very good explanation given in comments in the code.
Pragmatism needs to be permitted, but if you must break the rules you must explain why and it must be in the code for anyone else who maintains it to see. Thanks for these comments. I am in agreement with Michael Simpson. It leads to sloppiness in inexperienced developers. The goto keyword is too powerful of a construct. It enables a programmer to jump anywhere at anytime without consideration of the next programmer who may need to add additional code.
I personally adhere to the guidelines of providing a single exit from any block of code. There are exceptions to this: a break or continue statement within a while- or for-loop, for instance.
Bob Paddock rightly points out that clarity wins: this is often the sole justification to choose any programming language construct over another, though I still encounter performance issues specific to a tool chain requiring a surprising solution, from time to time.
I have on occasion designed small! Even maintaining a state variable eliminated by the choice of language construct would only have obfuscated behavior of the code, which typically fell naturally into an odd number of columns labels and braced pairs of optional guards and actions or transitions. The code would typically come to resemble a state-transition table, e. Not necessarily the most common case—indeed, worth the trouble of a written deviation—but it does tend to be one of the cases where an absolute ban can do more harm than good.
Note, though, all of these cases need exceptionally clear documentation as well as rigorous justification.
I support relaxing the restriction, particularly for exception handling as explained by Paddock and Heater. I would support banning goto into lower-level, nested blocks. Side story: I once had a colleague that would begin every program with a. He would create single functions of or more lines, but was meticulous to use the correct form if he was branching backwards or forwards to avoid getting lost in his own code.
He had a number of other quirks as well. I would take the view that gotos should not be used. If the reviewer s agree then the got can be permitted otherwise the reviewer s will demand a re-write. Everything in C has a purpose, you just need to know when to use, and when not. The goto is essential when you use C as an intermediate language for compiling DSLs. Though I never use goto, I recommend relaxing the ban on goto statements and allowing restricted use.
While deeply nested code is difficult to read, breaking out of two level deep nesting is a common occurrence and careful use of goto effectively makes this clearer.
This is especially true in the maintenance phase as defects are fixed and features are added. Obviously any variables accessed beyond the goto label must be initialized within a reasonable range of values, and that information should be provided within a comment. These variables should be declared and initialized at the top of a function.
It may make sense to only allow one goto label within a block or function, and that label must be below any goto statements. The obvious way to think about a process is how it will normally proceed.
Most modern high level languages provide native exception handling. I was ramdomming through xkcd and saw this one if also read some negative texts about them some years ago : What is actually wrong with it?
Because they lead to spaghetti code. In the past, programming languages didn't have while loops, if statements, etc. It lead to an unmaintainable mess. That's why the CS gods created methods, conditionals and loops. Structured programming was a revolution at the time. Nothing is wrong with goto if it is used properly. The reason it is "taboo" is because in the early days of C, programmers often coming from an assembly background would use goto to create incredibly hard-to-understand code. Most of the time, you can live without goto and be fine.
There are a few instances, however, where goto can be useful. The prime example is a case like:. Using a goto to jump out of a deeply-nested loop can often be cleaner than using a condition variable and checking it on every level. Using goto to implement subroutines is the main way it is abused. This creates so-called "spaghetti code" that is unnecessarily difficult to read and maintain. There is nothing wrong with goto in itself. It's a very useful construct in programming and has many valid uses.
The best that comes to mind is structured resource freeing in C programs. Where goto's go wrong is when they are abused. Abuse of gotos can lead to thoroughly unreadable and unmaintainable code.
In , Edsger Dijkstra wrote a famous letter to the editor of Communications of the ACM GOTO is considered harmful in which he laid out the case for structured programming with while loops and if When GOTO is used to substitute for these control structures, the result is very often spaghetti code.
Pretty much every programming language in use to day is a structured programming language, and use of GOTOs has been pretty much eliminated. In fact, Java, Scala, Ruby, and Python don't have a goto command at all. But generally its use should be restricted to specific design patterns that call for it in a controlled and recognized way.
The founder of the anti-goto movement is Edsger Dijskstra with his legendary "Goto Considered Harmful". To get you started you can goto ha ha! Whether you should or shouldn't use it is long-standing religious war. Including goto was part of the effort to reach that goal. Stack Overflow for Teams — Collaborate and share knowledge with a private group. Create a free Team What is Teams? Collectives on Stack Overflow. He argued that the use of unconditional branches, commonly known as goto statements, should be abolished from high level programming languages.
The animosity against goto statements is well-deserved. Dense sequences of statements laden with interwoven networks of goto statements are hard to understand and even harder to maintain. Although goto remains taboo, its use is still possible.
Is goto ever justified? Should it be completely wiped from the face of the Earth? I argue there are cases in C programs where goto is helpful. Unconditional branching is a tool. Some tools, such as chainsaws, are dangerous. This does not mean that chainsaws should be banned.
There are situations where careful use of a chainsaw is the best choice. When is goto a wise choice? Here are two scenarios where it has merit. C and other programming languages recognize the widespread need to leave a loop early.
C provides the break statement for this purpose. A break statement is a variant of goto. It is an unconditional branch that jumps out of its containing for , while , or switch , instead of to an explicit label.
Sometimes we would like to break out of more than one nested loop. Suppose we have inherited some code that prints the contents of a 3-by-3 array of integers:. Now suppose we have a new requirement that if any of the array elements are negative, we must immediately stop printing anything.
We want to break out of both loops. It is possible to use a flag to avoid a goto , like this:. But a more elegant way to handle this situation is to use a goto that exits both loops:. This is more concise and easier to understand than the preceding version of the code. It says what it means. It expresses the idea with less conceptual overhead.
C programs must detect and handle errors. When an error occurs, it is important to bail out while still cleaning up any dangling resources. The code should close any open files and free any allocated memory.
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