How to get to an outer while

[Richardcavell]

Hi everyone. I've written a search and replace routine in C99. I think it should work, but there is a point marked by the // where I want to restart the outer while loop. How do I do this?

Richard (TIA)

char *ptokens[][2] = 
{
   { "Find this" , "Replace with this" } ,
   { "Another one" , "Here's the replacement." } ,
   { 0 , 0 }
} ;

int searchandreplace ( char* psource , char* pdestination ) 
{
	while ( *psource != 0 )
	{
		int i = 0 ;

		while ( ptokens [i][0] != 0 )
		{
			char* ptoken = strstr ( psource , ptokens [i][0] ) ;
			if ( ptoken == psource )
			{
				strcpy ( pdestination , ptokens [i][1] ) ;
				psource += strlen ( ptokens [i][0] ) ;
				pdestination += strlen ( ptokens [i][1] ) ;
				// start outer while again
			}
			else
				i++ ;
		}

		*pdestination ++ = *psource ++ ;
	}

	*pdestination = 0 ;

	return 0 ;
}

[grumpy]

There is actually no direct way to jump back out through two levels of nested loops.

There are various indirect ways.

The simplest way, although it would make "anti-goto" zealots incredibly unhappy, is to place a label at the start of the outer loop, and then "goto that_label;".

Another way might involve using negative values of i as an indicator that the code needs to start again;

while ( *psource != '0' )
	{
		int i = 0;

		while ( i >= 0 && ptokens [i][0] != 0)
		{
			char* ptoken = strstr ( psource , ptokens [i][0] ) ;
			if ( ptoken == psource )
			{
				strcpy ( pdestination , ptokens [i][1] ) ;
				psource += strlen ( ptokens [i][0] ) ;
				pdestination += strlen ( ptokens [i][1] ) ;
				i = -1;   /*  signal breakout */
			}
			else
				i++ ;
		}

		if (i >= 0) *pdestination ++ = *psource ++ ;
	}

More generally, however, it would be better to restructure your code to reduce (or, better, eliminate if you can) the need to back out of multiple nested loops. Code that arbitrarily backs out of multiple nested loops tends to be somewhat difficult to understand, and therefore harder to get right - and rather fragile if you need to change the logic later on.