From -564418090617296406 X-Google-Thread: f78e5,1d1109cd86668825,start X-Google-Attributes: gidf78e5,public X-Google-Language: ENGLISH,ASCII-7-bit Path: g2news2.google.com!news4.google.com!news.glorb.com!news.alt.net!comp-std-cpp-robomod!not-for-mail From: "dstevel" Newsgroups: comp.std.c++ Subject: strtol const-ness problem Date: Sat, 12 Aug 2006 15:38:54 CST Organization: http://groups.google.com Lines: 64 Approved: Fergus Henderson , moderator of comp.std.c++ Message-ID: <1155392893.026182.121030@h48g2000cwc.googlegroups.com> Mime-Version: 1.0 Content-Type: text/plain; charset="iso-8859-1" X-Trace: posting.google.com 1155392896 12286 127.0.0.1 (12 Aug 2006 14:28:16 GMT) X-Complaints-To: groups-abuse@google.com NNTP-Posting-Date: Sat, 12 Aug 2006 14:28:16 +0000 (UTC) Return-Path: X-Authentication-Warning: mulga.csse.unimelb.edu.au: fjh set sender to devnull@stump.algebra.com using -f X-Robomod: STUMP, ichudov@algebra.com (Igor Chudov) X-Original-To: std-c++@mailman.ucar.edu Delivered-To: std-c++@mailman.ucar.edu User-Agent: G2/0.2 X-HTTP-UserAgent: Mozilla/5.0 (Windows; U; Windows NT 5.1; en-US; rv:1.8.0.6) Gecko/20060728 Firefox/1.5.0.6,gzip(gfe),gzip(gfe) Complaints-To: groups-abuse@google.com Injection-Info: h48g2000cwc.googlegroups.com; posting-host=71.193.233.44; posting-account=MidBUg0AAAA0r3VZXx8ZSe9LraA2fVzN X-Virus-Scanned: amavisd-new at ucar.edu X-Virus-Scanned: amavisd-new at csse.unimelb.edu.au X-Virus-Scanned: amavisd-new at csse.unimelb.edu.au Xref: g2news2.google.com comp.std.c++:3253 Note: This was originally posted in comp.lang.c++ and it was recommended that I post it to std so here it is. ======================= The signature for strtol is: strtol( const char*, char**, int) So.. if we start with a passed "const char*" (pointer to const char), then we can't create a non-const char pointer pointer to that const char pointer as in: void func( const char* a ) { // ERROR: invalid conversion from `const char**' to `char**' char** pa = &a; int i = strtol( a, pa, 10 ); } And here is another way of saying the same thing without temporary variables. void func( const char* a ) { // ERROR: invalid conversion from `const char**' to `char**' // ERROR: initializing argument 2 of `long int strtol... int i = strtol( a, &a, 10 ); } But you CAN do: void func( const char* a ) { int i = strtol( a, (char**)&a, 10 ); // OK } AND you can also do this: void func( const char* a ) { char* tmp; int i = strtol( a, &tmp, 10 ); // OK a = tmp; } This indirectly allows us to modify the original const char* a through the new pointer tmp since tmp will point into the character array a. It doesn't involve a hard cast, but it seems just as dangerous or even more so because it's not obvious what just happened. The calling function could see a change in the string pointed to by a, even though it's passed as pointer to const. Can someone help me figure out why this is OK? --- [ comp.std.c++ is moderated. To submit articles, try just posting with ] [ your news-reader. If that fails, use mailto:std-c++@ncar.ucar.edu ] [ --- Please see the FAQ before posting. --- ] [ FAQ: http://www.comeaucomputing.com/csc/faq.html ]