[Asterisk-Dev] fun with valgrind

[Dan Evans]

The interesting point here is that the C string library functions, with 
the exception of memmove, have undefined behavior for overlapping source 
and destination.  And this design potentially moves some characters 
several times; a different approach would move each character once or 
not at all.

Dan

Gilad Ben-Yossef wrote:
> Matthew Boehm wrote:
> 
>> /* substitute strings \t and \n into the apropriate characters */
>> tmpread = tmpwrite = emailbody;
>> while ((tmpwrite = strchr(tmpread,'\\'))) {
>>     int len = strlen("\n");
>>     switch (tmpwrite[1]) {
>>         case 'n':
>>             strncpy(tmpwrite+len,tmpwrite+2,strlen(tmpwrite+2)+1); 
>> <=== line
>> 5545
>>             strncpy(tmpwrite,"\n",len);
>>             break;
>>         case 't':
>>             strncpy(tmpwrite+len,tmpwrite+2,strlen(tmpwrite+2)+1); 
>> <=== line
>> 5549
>>             strncpy(tmpwrite,"\t",len);
>>             break;
>>         default:
>>             ast_log(LOG_NOTICE, "Substitution routine does not support 
>> this
>> character: %c\n",tmpwrite[1]);
>>     }
>>     tmpread = tmpwrite+len;
>> }
>>
>> Could somebody explain what is going on there? It seems as if the code is
>> replacing "\n" with "\n" and "\t" with "\t".
>>
> 
> That is exactly what it is doing - except that it replaces the literal 
> characters '\' and 't', for example, with the ASCII code for tab, which 
> in C is written '\t'.
> 
> In other words, the code in Asterisk that replcaes the characters "\t" 
> with the ASCII value for a tab works thanks to the fact that  the C 
> compiler does exactly the same thing in a kind of recursive way that 
> reminds me of Scheme programs... :-)
> 
> Gilad
>