How to break out of a loop from inside a switch?

You can use goto.

while ( ... ) {
   switch( ... ) {
     case ...:
         goto exit_loop;

   }
}
exit_loop: ;

An alternate solution is to use the keyword continue in combination with break, i.e.:

for (;;) {
    switch(msg->state) {
        case MSGTYPE:
            // code
            continue; // continue with loop
        case DONE:
            break;
    }
    break;
}

Use the continue statement to finish each case label where you want the loop to continue and use the break statement to finish case labels that should terminate the loop.

Of course this solution only works if there is no additional code to execute after the switch statement.

A neatish way to do this would be to put this into a function:

int yourfunc() {

    while(true) {

        switch(msg->state) {
        case MSGTYPE: // ... 
            break;
        // ... more stuff ...
        case DONE:
            return; 
        }

    }
}

Optionally (but 'bad practices'): as already suggested you could use a goto, or throw an exception inside the switch.

AFAIK there is no "double break" or similar construct in C++. The closest would be a goto - which, while it has a bad connotation to its name, exists in the language for a reason - as long as it's used carefully and sparingly, it's a viable option.

You could put your switch into a separate function like this:

bool myswitchfunction()
{
    switch(msg->state) {
    case MSGTYPE: // ... 
        break;
    // ... more stuff ...
    case DONE:
        return false; // **HERE, I want to break out of the loop itself**
    }
    return true;
}

while(myswitchfunction())
    ;

Even if you don't like goto, do not use an exception to exit a loop. The following sample shows how ugly it could be:

try {
  while ( ... ) {
    switch( ... ) {
      case ...:
        throw 777; // I'm afraid of goto
     }
  }
}
catch ( int )
{
}

I would use goto as in this answer. In this case goto will make code more clear then any other option. I hope that this question will be helpful.

But I think that using goto is the only option here because of the string while(true). You should consider refactoring of your loop. I'd suppose the following solution:

bool end_loop = false;
while ( !end_loop ) {
    switch( msg->state ) {
    case MSGTYPE: // ... 
        break;
    // ... more stuff ...
    case DONE:
        end_loop = true; break;
    }
}

Or even the following:

while ( msg->state != DONE ) {
    switch( msg->state ) {
    case MSGTYPE: // ... 
        break;
    // ... more stuff ...
}

There's no C++ construct for breaking out of the loop in this case.

Either use a flag to interrupt the loop or (if appropriate) extract your code into a function and use return.

No, C++ does not have a construct for this, given that the keyword "break" is already reserved for exiting the switch block. Alternatively a do..while() with an exit flag could suffice.

do { 
    switch(option){
        case 1: ..; break;
        ...
        case n: .. ;break;
        default: flag = false; break;
    }
} while(flag);

You could potentially use goto, but I would prefer to set a flag that stops the loop. Then break out of the switch.

Why not just fix the condition in your while loop, causing the problem to disappear?

while(msg->state != DONE)
{
    switch(msg->state) {
    case MSGTYPE: // ... 
        break;
    // ... more stuff ...
    case DONE:
        // We can't get here, but for completeness we list it.
        break; // **HERE, I want to break out of the loop itself**
    }
}

It amazes me how simple this is considering the depth of explanations... Here's all you need...

bool imLoopin = true;

while(imLoopin) {

    switch(msg->state) {

        case MSGTYPE: // ... 
            break;

        // ... more stuff ...

        case DONE:
            imLoopin = false;
            break;

    }

}

LOL!! Really! That's all you need! One extra variable!

I think;

while(msg->state != mExit) 
{
    switch(msg->state) 
    {
      case MSGTYPE: // ...
         break;
      case DONE:
      //  .. 
      //  ..
      msg->state =mExit;
      break;
    }
}
if (msg->state ==mExit)
     msg->state =DONE;

I got same problem and solved using a flag.

bool flag = false;
while(true) {
    switch(msg->state) {
    case MSGTYPE: // ... 
        break;
    // ... more stuff ...
    case DONE:
        flag = true; // **HERE, I want to break out of the loop itself**
    }
    if(flag) break;
}

Because the switch uses the break to break out from the switch (not from the while(1)), it needs the goto-statement:

while(1) {
    switch (*p) {
      case ' ':
        p++;
        break;
      case '\n':
        p++; *s=p; return(i);
      case '\0':
        *s=p; return(i);
      default:
        token[i]=p;
        i++;
        p++;
        goto ex1;
    };
  };
  ex1:

I can't add multiple case to same line like:

case ' ','\t':

it would be

case ' ': case '\t':

That's why maybe the break used here...

It looks the most frequent cases should be placed at the top of the list to make the program run faster. It may not have parallel execution for searching the different cases.

It is possible that the standard c then has missing some methods about this switching: https://blog.hackajob.co/better-c-switch-statements-for-a-range-of-values/ => allows you to use the <, >, <=, and >= operators in a switch expression

I was thinking that it should be (if c-language syntax changed) like:

switch (c) {
  case >= 5:
     ... op1
  endcase;
  case == 1:
  case == 3:
     ... op2
  endcase;
  default:
    ...
};

where op2 is executed when c is equal to 1 or 3 and when c is larger than or equal to 5 op1 is executed. Because comparison for equal or larger/smaller than would occur easily in similar manner.

  while(1) {
    switch (c) {
      case >= 2:
         ... op1
      case <= 5:
         ... op2
      break;
      default:
        ...
    };
  };

this case op1 is executed for c larger than 2 and op2 executed for 2<=c<=5 and break exits it from while-loop.

The simplest way to do it is to put a simple IF before you do the SWITCH , and that IF test your condition for exiting the loop .......... as simple as it can be

The break keyword in C++ only terminates the most-nested enclosing iteration or switch statement. Thus, you couldn't break out of the while (true) loop directly within the switch statement; however you could use the following code, which I think is an excellent pattern for this type of problem:

for (; msg->state != DONE; msg = next_message()) {
    switch (msg->state) {
    case MSGTYPE:
        //...
        break;

    //...
    }
}

If you needed to do something when msg->state equals DONE (such as run a cleanup routine), then place that code immediately after the for loop; i.e. if you currently have:

while (true) {
    switch (msg->state) {
    case MSGTYPE:
        //... 
        break;

    //...

    case DONE:
        do_cleanup();
        break;
    }

    if (msg->state == DONE)
        break;

    msg = next_message();
}

Then use instead:

for (; msg->state != DONE; msg = next_message()) {
    switch (msg->state) {
    case MSGTYPE:
        //...
        break;

    //...
    }
}

assert(msg->state == DONE);
do_cleanup();

while(MyCondition) {
switch(msg->state) {
case MSGTYPE: // ... 
    break;
// ... more stuff ...
case DONE:
   MyCondition=false; // just add this code and you will be out of loop.
    break; // **HERE, you want to break out of the loop itself**
}
}

Well its the crazy unruly homegrown cpp programmer with another one. The classy programmers have cringed against using terminating conditions inside loop body but I highly disagree. I qualify my belief with the fact that I used loops much more than the regular programmer, since I do text parsing manually and not with regex. Plus other kinds of situtations where I needed loops. So I understand the need for terminating conditions inside loops. Infact, even if I only have one condition, I may prefer a while(true) loop; in order to do all my code inside the loop body. eg:

while(true)
{
    if(condition)
    {
     // do something
     return;
    }

    // .... long body
}

This format allows persons to see what action is taken on loop termination immediately.

Anyhow, I will explain the BREAK_OUT_OF keyword. It allows you to break out of outer loops or switch statements, from within an inner loop or switch statement. This keyword is set to come in the next version of cpp, cpp 2026. But dont worry, for now you can emulate it in your primitive cpp compilers. Here are the steps.

Step 1: Download the BREAK_OUT_OF keyword package with the following command:

#define BREAK_OUT_OF(ID) goto STATEMENT##ID
#define S_ID(ID)
#define DEF_S_ID(ID) STATEMENT##ID:

Dont be fooled by the goto statement in the commands. Its not a regular goto statement that we all hate. Its a jmp statement in disguise.

Step 2: Now that you downloaded the compatibility package; when you need to break out of an outer statement from within an inner statement; you first give it an ID. You do this using S_ID keyword.

while(true) S_ID(first_loop)

Step 3: Place DEF_S_ID keyword immediately after statement body. Note that in the up coming cpp 26, This will automatically be done for us.

while(true) S_ID(first_loop)
{
}DEF_S_ID(first_loop)

Last Step: break out of outer loop from within inner loop using BREAK_OUT_OF keyword

while(true) S_ID(first_loop)
{
    switch(10) S_ID(1)
    {
     case 10: BREAK_OUT_OF(first_loop);
     case 0: BREAK_OUT_OF(1);
    }DEF_S_ID(1)
}DEF_S_ID(first_loop)

If I remember C++ syntax well, you can add a label to break statements, just like for goto. So what you want would be easily written:

while(true) {
    switch(msg->state) {
    case MSGTYPE: // ...
        break;
    // ... more stuff ...
    case DONE:
        break outofloop; // **HERE, I want to break out of the loop itself**
    }
}

outofloop:
// rest of your code here