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• not working function with no errors

  - by aya

  hello.. I've implemented a function to display an avl tree after inserting nodes into it like this template void AVLtree::display() const { display(Proot); } template void AVLtree::display(Node * ptr) const { if(ptr==0) return ; cout<value<<" "; display(ptr-Pleft); display(ptr-Pright); } after compiling,there were no errors ,the program worked but nothing were printed on the screen help me please....!! thanks

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• Can I make a pointer to the code, and pass to the next instruction?

  - by drigoSkalWalker

  Like this link http://gcc.gnu.org/onlinedocs/gcc-3.3.1/gcc/Labels-as-Values.html I can get the memory address of an label, so if I declare a label, get your address, and add your address, i will pass to next instruction? some ilustration int main () { void *ptr; label: instruction 1; instruction 2; ptr = &&label; // So if I do it... ptr = ptr + 1; // I will get the instruction 2 correct?? Thanks for all answers.

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• Convert a number from string to integer without using inbuilt function

  - by Raja

  I am trying this technique but error is coming. Please help me to convert a number from string to integer. #include<iostream> using namespace std; int main() { char *buffer[80]; int a; cout<<"enter the number"; cin.get(buffer,79); char *ptr[80] = &buffer; while(*ptr!='\0') { a=(a*10)+(*ptr-48); } cout<<"the value"<<a; delete ptr[]; return 0; } Errors are: error C2440: 'initializing' : cannot convert from 'char ()[80]' to 'char *[80]' error C2440: '=' : cannot convert from 'char *' to 'int'

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• how to copy an array into somewhere else in the memory by using the pointer

  - by user2758510

  I am completely new in c++ programming. I want to copy the array called distances into where pointer is pointing to and then I want to print out the resul to see if it is worked or not. this is what I have done: int distances[4][6]={{1,0,0,0,1,0},{1,1,0,0,1,1},{1,0,0,0,0,0},{1,1,0,1,0,0}}; int *ptr; ptr = new int[sizeof(distances[0])]; for(int i=0; i<sizeof(distances[0]); i++){ ptr=distances[i]; ptr++; } I do not know how to print out the contents of the pointer to see how it works.

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• hash table with chaining method program freezing

  - by Justin Carrey

  I am implementing hash table in C using linked list chaining method. The program compiles but when inserting a string in hash table, the program freezes and gets stuck. The program is below: struct llist{ char *s; struct llist *next; }; struct llist *a[100]; void hinsert(char *str){ int strint, hashinp; strint = 0; hashinp = 0; while(*str){ strint = strint+(*str); } hashinp = (strint%100); if(a[hashinp] == NULL){ struct llist *node; node = (struct llist *)malloc(sizeof(struct llist)); node->s = str; node->next = NULL; a[hashinp] = node; } else{ struct llist *node, *ptr; node = (struct llist *)malloc(sizeof(struct llist)); node->s = str; node->next = NULL; ptr = a[hashinp]; while(ptr->next != NULL){ ptr = ptr->next; } ptr->next = node; } } void hsearch(char *strsrch){ int strint1, hashinp1; strint1 = 0; hashinp1 = 0; while(*strsrch){ strint1 = strint1+(*strsrch); } hashinp1 = (strint1%100); struct llist *ptr1; ptr1 = a[hashinp1]; while(ptr1 != NULL){ if(ptr1->s == strsrch){ cout << "Element Found\n"; break; } else{ ptr1 = ptr1->next; } } if(ptr1 == NULL){ cout << "Element Not Found\n"; } } hinsert() is to insert elements into hash and hsearch is to search an element in the hash. Hash function is written inside hinsert() itself. In the main(), what i am initializing all the elements in a[] to be NULL like this: for(int i = 0;i < 100; i++){ a[i] = NULL; } Help is very much appreciated. Thanks !

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• delete vs NULL vs free in c++

  - by hero

  what is the difference between deleting a pointer and setting it to null and freeing it. delete ptr; ptr=NULL; free(ptr);

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• I am trying to access the individual bytes in a floating point number and I am getting unexpected results

  - by oweinh

  So I have this so far: #include <iostream> #include <string> #include <typeinfo> using namespace std; int main () { float f = 3.45; // just an example fp# char* ptr = (char*)&f; // a character pointer to the first byte of the fp#? cout << int(ptr[0]) << endl; // these lines are just to see if I get what I cout << int(ptr[1]) << endl; // am looking for... I want ints that I can cout << int(ptr[2]) << endl; // otherwise manipulate. cout << int(ptr[3]) << endl; } the result is: -51 -52 92 64 so obviously -51 and -52 are not in the byte range that I would expect for a char... I have taken information from similar questions to arrive at this code and from all discussions, a conversion from char to int is straightforward. So why negative values? I am trying to look at a four-byte number, therefore I would expect 4 integers, each in the range 0-255. I am using Codeblocks 13.12 with gcc 4.8.1 with option -std=C++11 on a Windows 8.1 device.

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• Cannot determine why pointer variable will not address elements in a string in this program?

  - by Smith Will Suffice

  I am attempting to utilize a pointer variable to access elements of a string and there are issues with my code generating a compilation error: #include <stdio.h> #define MAX 29 char arrayI[250]; char *ptr; int main(void) { ptr = arrayI; puts("Enter string to arrayI: up to 29 chars:\n"); fgets(arrayI, MAX, stdin); printf("\n Now printing array by pointer:\n"); printf("%s", *ptr); ptr = arrayI[1]; //(I set the pointer to the second array char element) printf("%c", *ptr); //Here is where I was wanting to use my pointer to //point to individual array elements. return 0; } My compiler crieth: [Warning] assignment makes pointer from integer without a cast [enabled by default] I do not see where my pointer was ever assigned to the integer data type? Could someone please explain why my attempt to implement a pointer variable is failing? Thanks all!

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• warning: format ‘%s’ expects type ‘char *’, but argument 2 has type ‘int’

  - by pyz

  code: #include <stdio.h> #include <stdlib.h> #include <netdb.h> #include <sys/socket.h> int main(int argc, char **argv) { char *ptr, **pptr; struct hostent *hptr; char str[32]; //ptr = argv[1]; ptr = "www.google.com"; if ((hptr = gethostbyname(ptr)) == NULL) { printf("gethostbyname error for host:%s\n", ptr); } printf("official hostname:%s\n", hptr->h_name); for (pptr = hptr->h_aliases; *pptr != NULL; pptr++) printf(" alias:%s\n", *pptr); switch (hptr->h_addrtype) { case AF_INET: case AF_INET6: pptr = hptr->h_addr_list; for (; *pptr != NULL; pptr++) printf(" address:%s\n", inet_ntop(hptr->h_addrtype, *pptr, str, sizeof(str))); break; default: printf("unknown address type\n"); break; } return 0; } compiler output below: zhumatoMacBook:CProjects zhu$ gcc gethostbynamedemo.c gethostbynamedemo.c: In function ‘main’: gethostbynamedemo.c:31: warning: format ‘%s’ expects type ‘char *’, but argument 2 has type ‘int’

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• Identifying the cause of my DNS failure (domain not propagating)

  - by thejartender

  I have set up a DNS server with the help of two helpful tutorials: http://linuxconfig.org/linux-dns-server-bind-configuration http://ulyssesonline.com/2007/11/07/how-to-setup-a-dns-server-in-ubuntu/ I am using: Ubuntu Bind9 and had issues I tried negating on my own thanks to a question I posted here earlier that pointed out my mistake of using rfc 1918 addresses in my previous SOA record: $TTL 3D @ IN SOA ns.thejarbar.org. email. ( 13112012 28800 3600 604800 38400 ); thejarbar.org. IN A 10.0.0.42 @ IN NS ns.thejarbar,org. yuccalaptop IN A 10.0.0.19 ns IN A 10.0.0.42 gw IN A 10.0.0.138 www IN CNAME thejarbar.org. $TTL 600 0.0.10.in-addr.arpa. IN SOA ns.thejarbar.org. email. ( 13112012 28800 3600 604800 38400 ); 0.0.10.in-addr.arpa. IN NS ns.thejarbar.org. 42 IN PTR thejarbar.org. 19 IN PTR yuccalaptop.thejarbar.org. 138 IN PTR gw.thejarbar.org. I read the ranges that are used under rfc 1918 and modified my routers resource pool to assign LAN devices IP(s) within the 30.0.0.0 range and now modified my SOA to: $TTL 600 @ IN SOA ns.thejarbar.org. email. ( 13112012 28800 3600 604800 38400 ); thejarbar.org. IN A 30.0.0.42 @ IN NS ns.thejarbar,org. yuccalaptop IN A 10.0.0.19 ns IN A 30.0.0.42 gw IN A 30.0.0.138 www IN CNAME thejarbar.org. $TTL600 0.0.10.in-addr.arpa. IN SOA ns.thejarbar.org. email. ( 13112012 28800 3600 604800 38400 ); 0.0.30.in-addr.arpa. IN NS ns.thejarbar.org. 42 IN PTR thejarbar.org. 19 IN PTR yuccalaptop.thejarbar.org. 138 IN PTR gw.thejarbar.org. I can ping my nameserverver ns.thejarbar.organd it gives me the correct isp IP address, but my domain never seems to propagate to my nameserver. I have searched for a concise tutorial that covers setting up a DNS with a nameserver that hosts (my) or the site. I am fully aware that this is not recommended and am using this for my learning purposes. Getting to the question, due to the lack of information in tutorials I looked at (nothing about rfc 1918 and no example of swapping these with ISP IP) is my router modification going to help me as it does not seem to be. I have also tried as recommended using my ISP IP instead of the values I posted. My site never propagated to my nameserver. What could be causing this? I have run dig thejarbar.org @88.89.190.171 and get an authorative response. Can anyone assist me with the final steps I may be missing here?

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• C++ Conceptual problem with (Pointer) Pointers

  - by Ptr

  I have a structure usually containing a pointer to an int. However, in some special cases, it is necessary that this int pointer points to another pointer which then points to an int. Wow: I mentioned the word pointer 5 times so far! Is this even possible? I thought about it that way: Instead of using a second int pointer, which is most likely not possible as my main int pointer can only point to an int and not to another int pointer, I could make it a reference like this: int intA = 1; int intB = 2; int& intC = intB; int* myPointers[ 123 ]; myPointers[ 0 ] = &intA; myPointers[ 1 ] = &intB; myPointers[ 3 ] = &intC; So the above would do what I want: The reference to intB (intC) behaves quite like I want it to (If it gets changed it also changes intB) The problem: I can't change references once they are set, right? Or is there a way? Everything in short: How do I get a value to work with * (pointers) and ** (pointers to pointers)?

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• domain/IN: has no NS records

  - by thejartender

  I have set up a home web server using Ubuntu 12.10 and I can safely say that it works with regards to router forwarding and ports being found. I know this, because switched my hosting provider's VPS SOA record to use my ISP IP with an 'A' value and had my website running from home. This verified that my server was configured correctly so I started what I believe to be the final step in making my old desktop into a full DNS server. I found this tutorial that got me started My LAN network consists of the following: My router with a gateway of 10.0.0.zzz My server with an IP of 10.0.0.xxx A laptop with an IP of 10.0.0.yyy Step 1: I installed bind via sudo apt-get install bind9 Step2: I configured /etc/bind/named.conf.local with: zone "sognwebdesign.no" { type master; file "/etc/bind/zones/sognwebdesign.no.db"; }; zone "0.0.10.in-addr.arpa" { type master; file "/etc/bind/zones/rev.0.0.10.in-addr.arpa"; }; Step3: Updated /etc/bind/named.conf.options with two ISP DNS addresses Step 4: Updated /etc/resolv.confwith: nameserver 10.0.0.xxx search lan search sognwebdesign.no Step5: created a ``/etc/bind/zones directory Step6: Created /etc/bind/zones/sognwebdesign.no.dbwith: $TTL 3D @ IN SOA ns.sognwebdesign.no. admin.sognwebdesign.no. ( 2007062001 28800 3600 604800 38400 ); sognwebdesign.no. IN NS ns1.sognwebdesign.no. sognwebdesign.no. IN NS ns2.sognwebdesign.no. sognwebdesign.no. IN NS ns3.sognwebdesign.no. NS1 IN A 10.0.0.1 NS2 IN A 10.0.0.2 NS3 IN A 10.0.0.3 www IN A 10.0.0.4 yuccalaptop IN A 10.0.0.19 gw IN A 10.0.0.138 TXT "Network Gateway" Step 7: created/etc/bind/zones/rev.0.0.10.in-addr.arpawith: $TTL 3D @ IN SOA ns.sognwebdesign.no. admin.sognwebdesign.no. ( 2007062001 28800 604800 604800 86400 ); zzz IN PTR gw.sognwebdesign.no. 1 IN PTR ns1.sognwebdesign.no. 2 IN PTR ns2.sognwebdesign.no. 3 IN PTR ns3.sognwebdesign.no. yyy IN PTR yuccalaptop.sognwebdesign.no. I then restart bind and dig-x sognwebdesign.no and it works Lastly I perform named-checkzoneon each of my zone files, but me reverse zone fail fails with: sognwedesign.no/IN: has no NS records Can anyone explain what I am doing wrong here or assist me in getting this configured correctly?

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• Passing a template func. as a func. ptr to an overloaded func. - is there a way to compile this code

  - by LoudNPossiblyRight

  Just a general c++ curiosity: This code below shouldn't compile because it's impossible to know which to instantiate: temp(const int&) or temp(const string&) when calling func(temp) - this part i know. What i would like to know is if there is anything i can do to the line marked PASSINGLINE to get the compiler to deduce that i want FPTR1 called and not FPTR2 ? #include<iostream> using std::cout; using std::endl; /*FPTR1*/ void func(void(*fptr)(const int&)){ fptr(1001001);} /*FPTR2*/ void func(void(*fptr)(const string&)){ fptr("1001001"); } template <typename T> void temp(const T &t){ cout << t << endl; } int main(){ /*PASSINGLINE*/ func(temp); return 0; } Thank you.

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• How can I generate a view or projection matrix for OpenGL 3.+

  - by Ken

  I'm transitioning from OpenGL 2 to OpenGL 3.+ and to GLSL 1.5. I'm trying to avoid using the deprecated features. My question how do we now generate the view or projection matrix. I was using the matrix stack to calculate the projection matrix for me; GLfloat ptr[16]; gluPerspective(...); glGetFloatv(GL_MODELVIEW_MATRIX, ptr); //then pass ptr via a uniform to the shader But obviously the matrix stack is deprecated. So this approach is not the best an option going forward. I have the 'Red Book', 7th ed, which covers 3.0 & 3.1 and it still uses the deprecated matrix functions in it's examples. I could write some utility-code myself to generate the matrices. But I don't want to re-invent this particular wheel, especially when this functionality is required for every 3D graphics program. What is the accepted way to generate world,view & projection matrices for OpenGL? Is there an emerging 'standard' library for this? Or is there some other hidden (to me) functionality in OpenGL/GLSL which I have overlooked?

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• Does RDNS for mail server have to match the mail server hostname exactly?

  - by threecheeseopera

  Typically when setting up a mail server, I create an rDNS record for the mail server IP to match the mail server hostname (ex: mail.example.com). Can I instead set the rDNS ptr to match the parent domain (e.g. example.com), if this server is being used for multiple purposes, and still send mail successfully (i.e. not be classified as spam b/c of mismatched rDNS)? Thanks! EDIT: The article at http://en.wikipedia.org/wiki/Forward_Confirmed_reverse_DNS seems to indicate that it might be more complicated than I had thought. For instance, 1) I did not know that you could have multiple PTR records for a given IP; 2) it appears that as long as each PTR record matches an A record, everything is good (basically nullifying my question). Would you agree?

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• Run script when POST data is sent to Apache

  - by Nathan Adams

  Among my several years of running servers there seems to be a pattern with most spam activity. My question/idea is that is there a way to tell Apache to run a script when POST data is detected? What I would want to do is perform a reverse DNS lookup on the client's IP address, and then perform a DNS lookup on the hostname in the PTR record. Afterwards, perform some checks, excuse the pseudo-code: if PTR does not exist: deny POST request if IP of PTR hostname = client's IP Allow POST request else deny POST request Though I don't care about GET requests, even though they can be just as malicious, this idea is targeted towards spam comments which use POST data to send the comment data to the web server. In order to make sure there isn't much of a time delay, I would run my own recursive DNS server. Please do note, this isn't meant to be a sliver bullet to spam, but it should decrease the volume. Possible or impossible?

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• What does the Sys_PageIn() function do in Quake?

  - by Philip

  I've noticed in the initialization process of the original Quake the following function is called. volatile int sys_checksum; // **lots of code** void Sys_PageIn(void *ptr, int size) { byte *x; int j,m,n; //touch all memory to make sure its there. The 16-page skip is to //keep Win 95 from thinking we're trying to page ourselves in (we are //doing that, of course, but there's no reason we shouldn't) x = (byte *)ptr; for (n=0 ; n<4 ; n++) { for (m=0; m<(size - 16 * 0x1000) ; m += 4) { sys_checksum += *(int *)&x[m]; sys_checksum += *(int *)&x[m + 16 * 0x10000]; } } } I think I'm just not familiar enough with paging to understand this function. the void* ptr passed to the function is a recently malloc()'d piece of memory that is size bytes big. This is the whole function - j is an unreferenced variable. My best guess is that the volatile int sys_checksum is forcing the system to physically read all of the space that was just malloc()'d, perhaps to ensure that these spaces exist in virtual memory? Is this right? And why would someone do this? Is it for some antiquated Win95 reason?

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• gem install of mongrel

  - by atlantis

  I initiated myself into rails development yesterday. I installed ruby 1.9.1 , rubygems and rails. Running 'gem install mongrel' worked fine and ostensibly installed mongrel too. I am slightly puzzled because script/server starts webrick by default 'which mongrel' returns nothing 'locate mongrel' returns lots of entries like . /Developer/SDKs/MacOSX10.5.sdk/System/Library/Frameworks/Ruby.framework/Versions/1.8/usr/lib/ruby/gems/1.8/gems/mongrel-1.0.1 /Developer/SDKs/MacOSX10.5.sdk/System/Library/Frameworks/Ruby.framework/Versions/1.8/usr/lib/ruby/gems/1.8/gems/mongrel-1.0.1/lib /Developer/SDKs/MacOSX10.5.sdk/System/Library/Frameworks/Ruby.framework/Versions/1.8/usr/lib/ruby/gems/1.8/gems/mongrel-1.0.1/lib/mongrel . . . /usr/local/bin/mongrel_rails /usr/local/lib/ruby/gems/1.9.1/cache/mongrel-1.1.5.gem /usr/local/lib/ruby/gems/1.9.1/doc/actionpack-2.3.2/rdoc/files/lib/action_controller/vendor/rack-1_0/rack/handler/evented_mongrel_rb.html /usr/local/lib/ruby/gems/1.9.1/doc/actionpack-2.3.2/rdoc/files/lib/action_controller/vendor/rack-1_0/rack/handler/mongrel_rb.html /usr/local/lib/ruby/gems/1.9.1/doc/actionpack-2.3.2/rdoc/files/lib/action_controller/vendor/rack-1_0/rack/handler/swiftiplied_mongrel_rb.html /usr/local/lib/ruby/gems/1.9.1/gems/actionpack-2.3.2/lib/action_controller/vendor/rack-1.0/rack/handler/evented_mongrel.rb /usr/local/lib/ruby/gems/1.9.1/gems/actionpack-2.3.2/lib/action_controller/vendor/rack-1.0/rack/handler/mongrel.rb /usr/local/lib/ruby/gems/1.9.1/gems/actionpack-2.3.2/lib/action_controller/vendor/rack-1.0/rack/handler/swiftiplied_mongrel.rb /usr/local/lib/ruby/gems/1.9.1/gems/mongrel-1.1.5 . . . Does look like I have mongrel installed (both the default installation and my custom install). So why doesn't which mongrel return something. Also trying to reinstall mongrel using 'gem install mongrel' returns throws its own set of exceptions : Building native extensions. This could take a while... ERROR: Error installing mongrel: ERROR: Failed to build gem native extension. /usr/local/bin/ruby extconf.rb install mongrel checking for main() in -lc... yes creating Makefile make gcc -I. -I/usr/local/include/ruby-1.9.1/i386-darwin9.7.0 -I/usr/local/include/ruby-1.9.1/ruby/backward -I/usr/local/include/ruby-1.9.1 -I. -D_XOPEN_SOURCE -D_DARWIN_C_SOURCE -fno-common -D_XOPEN_SOURCE=1 -O2 -g -Wall -Wno-parentheses -fno-common -pipe -fno-common -o http11.o -c http11.c http11.c: In function 'http_field': http11.c:77: error: 'struct RString' has no member named 'ptr' http11.c:77: error: 'struct RString' has no member named 'len' http11.c:77: warning: left-hand operand of comma expression has no effect http11.c:77: warning: statement with no effect http11.c: In function 'header_done': http11.c:172: error: 'struct RString' has no member named 'ptr' http11.c:174: error: 'struct RString' has no member named 'ptr' http11.c:176: error: 'struct RString' has no member named 'ptr' http11.c:177: error: 'struct RString' has no member named 'len' http11.c: In function 'HttpParser_execute': http11.c:298: error: 'struct RString' has no member named 'ptr' http11.c:299: error: 'struct RString' has no member named 'len' make: *** [http11.o] Error 1

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• `gem install mongrel` fails with ruby 1.9.1

  - by atlantis

  I initiated myself into rails development yesterday. I installed ruby 1.9.1, rubygems and rails. Running gem install mongrel worked fine and ostensibly installed mongrel too. I am slightly puzzled because: script/server starts webrick by default which mongrel returns nothing locate mongrel returns lots of entries like /Developer/SDKs/MacOSX10.5.sdk/System/Library/Frameworks/Ruby.framework/Versions/1.8/usr/lib/ruby/gems/1.8/gems/mongrel-1.0.1 /Developer/SDKs/MacOSX10.5.sdk/System/Library/Frameworks/Ruby.framework/Versions/1.8/usr/lib/ruby/gems/1.8/gems/mongrel-1.0.1/lib /Developer/SDKs/MacOSX10.5.sdk/System/Library/Frameworks/Ruby.framework/Versions/1.8/usr/lib/ruby/gems/1.8/gems/mongrel-1.0.1/lib/mongrel . . . /usr/local/bin/mongrel_rails /usr/local/lib/ruby/gems/1.9.1/cache/mongrel-1.1.5.gem /usr/local/lib/ruby/gems/1.9.1/doc/actionpack-2.3.2/rdoc/files/lib/action_controller/vendor/rack-1_0/rack/handler/evented_mongrel_rb.html /usr/local/lib/ruby/gems/1.9.1/doc/actionpack-2.3.2/rdoc/files/lib/action_controller/vendor/rack-1_0/rack/handler/mongrel_rb.html /usr/local/lib/ruby/gems/1.9.1/doc/actionpack-2.3.2/rdoc/files/lib/action_controller/vendor/rack-1_0/rack/handler/swiftiplied_mongrel_rb.html /usr/local/lib/ruby/gems/1.9.1/gems/actionpack-2.3.2/lib/action_controller/vendor/rack-1.0/rack/handler/evented_mongrel.rb /usr/local/lib/ruby/gems/1.9.1/gems/actionpack-2.3.2/lib/action_controller/vendor/rack-1.0/rack/handler/mongrel.rb /usr/local/lib/ruby/gems/1.9.1/gems/actionpack-2.3.2/lib/action_controller/vendor/rack-1.0/rack/handler/swiftiplied_mongrel.rb /usr/local/lib/ruby/gems/1.9.1/gems/mongrel-1.1.5 . . . Does look like I have mongrel installed (both the default installation and my custom install). So why doesn't which mongrel return something. Also trying to reinstall mongrel using gem install mongrel returns throws its own set of exceptions: Building native extensions. This could take a while... ERROR: Error installing mongrel: ERROR: Failed to build gem native extension. /usr/local/bin/ruby extconf.rb install mongrel checking for main() in -lc... yes creating Makefile make gcc -I. -I/usr/local/include/ruby-1.9.1/i386-darwin9.7.0 -I/usr/local/include/ruby-1.9.1/ruby/backward -I/usr/local/include/ruby-1.9.1 -I. -D_XOPEN_SOURCE -D_DARWIN_C_SOURCE -fno-common -D_XOPEN_SOURCE=1 -O2 -g -Wall -Wno-parentheses -fno-common -pipe -fno-common -o http11.o -c http11.c http11.c: In function 'http_field': http11.c:77: error: 'struct RString' has no member named 'ptr' http11.c:77: error: 'struct RString' has no member named 'len' http11.c:77: warning: left-hand operand of comma expression has no effect http11.c:77: warning: statement with no effect http11.c: In function 'header_done': http11.c:172: error: 'struct RString' has no member named 'ptr' http11.c:174: error: 'struct RString' has no member named 'ptr' http11.c:176: error: 'struct RString' has no member named 'ptr' http11.c:177: error: 'struct RString' has no member named 'len' http11.c: In function 'HttpParser_execute': http11.c:298: error: 'struct RString' has no member named 'ptr' http11.c:299: error: 'struct RString' has no member named 'len' make: *** [http11.o] Error 1

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• wrapping boost::ublas with swig

  - by leon

  I am trying to pass data around the numpy and boost::ublas layers. I have written an ultra thin wrapper because swig cannot parse ublas' header correctly. The code is shown below #include <boost/numeric/ublas/vector.hpp> #include <boost/numeric/ublas/matrix.hpp> #include <boost/lexical_cast.hpp> #include <algorithm> #include <sstream> #include <string> using std::copy; using namespace boost; typedef boost::numeric::ublas::matrix<double> dm; typedef boost::numeric::ublas::vector<double> dv; class dvector : public dv{ public: dvector(const int rhs):dv(rhs){;}; dvector(); dvector(const int size, double* ptr):dv(size){ copy(ptr, ptr+sizeof(double)*size, &(dv::data()[0])); } ~dvector(){} }; with the SWIG interface that looks something like %apply(int DIM1, double* INPLACE_ARRAY1) {(const int size, double* ptr)} class dvector{ public: dvector(const int rhs); dvector(); dvector(const int size, double* ptr); %newobject toString; char* toString(); ~dvector(); }; I have compiled them successfully via gcc 4.3 and vc++9.0. However when I simply run a = dvector(array([1.,2.,3.])) it gives me a segfault. This is the first time I use swigh with numpy and not have fully understanding between the data conversion and memory buffer passing. Does anyone see something obvious I have missed? I have tried to trace through with a debugger but it crashed within the assmeblys of python.exe. I have no clue if this is a swig problem or of my simple wrapper. Anything is appreciated.

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• How to obtain a pointer out of a C++ vtable?

  - by Josh Haberman

  Say you have a C++ class like: class Foo { public: virtual ~Foo() {} virtual DoSomething() = 0; }; The C++ compiler translates a call into a vtable lookup: Foo* foo; // Translated by C++ to: // foo->vtable->DoSomething(foo); foo->DoSomething(); Suppose I was writing a JIT compiler and I wanted to obtain the address of the DoSomething() function for a particular instance of class Foo, so I can generate code that jumps to it directly instead of doing a table lookup and an indirect branch. My questions are: Is there any standard C++ way to do this (I'm almost sure the answer is no, but wanted to ask for the sake of completeness). Is there any remotely compiler-independent way of doing this, like a library someone has implemented that provides an API for accessing a vtable? I'm open to completely hacks, if they will work. For example, if I created my own derived class and could determine the address of its DoSomething method, I could assume that the vtable is the first (hidden) member of Foo and search through its vtable until I find my pointer value. However, I don't know a way of getting this address: if I write &DerivedFoo::DoSomething I get a pointer-to-member, which is something totally different. Maybe I could turn the pointer-to-member into the vtable offset. When I compile the following: class Foo { public: virtual ~Foo() {} virtual void DoSomething() = 0; }; void foo(Foo *f, void (Foo::*member)()) { (f->*member)(); } On GCC/x86-64, I get this assembly output: Disassembly of section .text: 0000000000000000 <_Z3fooP3FooMS_FvvE>: 0: 40 f6 c6 01 test sil,0x1 4: 48 89 74 24 e8 mov QWORD PTR [rsp-0x18],rsi 9: 48 89 54 24 f0 mov QWORD PTR [rsp-0x10],rdx e: 74 10 je 20 <_Z3fooP3FooMS_FvvE+0x20> 10: 48 01 d7 add rdi,rdx 13: 48 8b 07 mov rax,QWORD PTR [rdi] 16: 48 8b 74 30 ff mov rsi,QWORD PTR [rax+rsi*1-0x1] 1b: ff e6 jmp rsi 1d: 0f 1f 00 nop DWORD PTR [rax] 20: 48 01 d7 add rdi,rdx 23: ff e6 jmp rsi I don't fully understand what's going on here, but if I could reverse-engineer this or use an ABI spec I could generate a fragment like the above for each separate platform, as a way of obtaining a pointer out of a vtable.

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• Memory corruption in System.Move due to changed 8087CW mode (png + stretchblt)

  - by André Mussche

  I have strange a memory corruption problem. After many hours debugging and trying I think I found something. For example: I do a simple string assignment: sTest := 'SET LOCK_TIMEOUT '; However, the result sometimes becomes: sTest = 'SET LOCK'#0'TIMEOUT ' So, the _ gets replaced by an 0 byte. I have seen this happening once (reproducing is tricky, dependent on timing) in the System.Move function, when it uses the FPU stack (fild, fistp) for fast memory copy (in case of 9 till 32 bytes to move): ... @@SmallMove: {9..32 Byte Move} fild qword ptr [eax+ecx] {Load Last 8} fild qword ptr [eax] {Load First 8} cmp ecx, 8 jle @@Small16 fild qword ptr [eax+8] {Load Second 8} cmp ecx, 16 jle @@Small24 fild qword ptr [eax+16] {Load Third 8} fistp qword ptr [edx+16] {Save Third 8} ... Using the FPU view and 2 memory debug views (Delphi - View - Debug - CPU - Memory) I saw it going wrong... once... could not reproduce however... This morning I read something about the 8087CW mode, and yes, if this is changed into $27F I get memory corruption! Normally it is $133F: The difference between $133F and $027F is that $027F sets up the FPU for doing less precise calculations (limiting to Double in stead of Extended) and different infiniti handling (which was used for older FPU’s, but is not used any more). Okay, now I found why but not when! I changed the working of my AsmProfiler with a simple check (so all functions are checked at enter and leave): if Get8087CW = $27F then //normally $1372? if MainThreadID = GetCurrentThreadId then //only check mainthread DebugBreak; I "profiled" some units and dll's and bingo (see stack): Windows.StretchBlt(3372289943,0,0,514,345,4211154027,0,0,514,345,13369376) pngimage.TPNGObject.DrawPartialTrans(4211154027,(0, 0, 514, 345, (0, 0), (514, 345))) pngimage.TPNGObject.Draw($7FF62450,(0, 0, 514, 345, (0, 0), (514, 345))) Graphics.TCanvas.StretchDraw((0, 0, 514, 345, (0, 0), (514, 345)),$7FECF3D0) ExtCtrls.TImage.Paint Controls.TGraphicControl.WMPaint((15, 4211154027, 0, 0)) So it is happening in StretchBlt... What to do now? Is it a fault of Windows, or a bug in PNG (included in D2007)? Or is the System.Move function not failsafe?

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• How to access a matrix in a matlab struct's field from a mex function?

  - by B. Ruschill

  I'm trying to figure out how to access a matrix that is stored in a field in a matlab structure from a mex function. That's awfully long winded... Let me explain: I have a matlab struct that was defined like the following: matrixStruct = struct('matrix', {4, 4, 4; 5, 5, 5; 6, 6 ,6}) I have a mex function in which I would like to be able to receive a pointer to the first element in the matrix (matrix[0][0], in c terms), but I've been unable to figure out how to do that. I have tried the following: /* Pointer to the first element in the matrix (supposedly)... */ double *ptr = mxGetPr(mxGetField(prhs[0], 0, "matrix"); /* Incrementing the pointer to access all values in the matrix */ for(i = 0; i < 3; i++){ printf("%f\n", *(ptr + (i * 3))); printf("%f\n", *(ptr + 1 + (i * 3))); printf("%f\n", *(ptr + 2 + (i * 3))); } What this ends up printing is the following: 4.000000 0.000000 0.000000 0.000000 0.000000 0.000000 0.000000 0.000000 0.000000 I have also tried variations of the following, thinking that perhaps it was something wonky with nested function calls, but to no avail: /* Pointer to the first location of the mxArray */ mxArray *fieldValuePtr = mxGetField(prhs[0], 0, "matrix"); /* Get the double pointer to the first location in the matrix */ double *ptr = mxGetPr(fieldValuePtr); /* Same for loop code here as written above */ Does anyone have an idea as to how I can achieve what I'm trying to, or what I am potentially doing wrong? Thanks! Edit: As per yuk's comment, I tried doing similar operations on a struct that has a field called array which is a one-dimensional array of doubles. The struct containing the array is defined as follows: arrayStruct = struct('array', {4.44, 5.55, 6.66}) I tried the following on the arrayStruct from within the mex function: mptr = mxGetPr(mxGetField(prhs[0], 0, "array")); printf("%f\n", *(mptr)); printf("%f\n", *(mptr + 1)); printf("%f\n", *(mptr + 2)); ...but the output followed what was printed earlier: 4.440000 0.000000 0.000000

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• Determining if Memory Pointer is Valid - C++

  - by Jim Fell

  It has been my observation that if free( ptr ) is called where ptr is not a valid pointer to system-allocated memory, an access violation occurs. Let's say that I call free like this: LPVOID ptr = (LPVOID)0x12345678; free( ptr ); This will most definitely cause an access violation. Is there a way to test that the memory location pointed to by ptr is valid system-allocated memory? It seems to me that the the memory management part of the Windows OS kernel must know what memory has been allocated and what memory remains for allocation. Otherwise, how could it know if enough memory remains to satisfy a given request? (rhetorical) That said, it seems reasonable to conclude that there must be a function (or set of functions) that would allow a user to determine if a pointer is valid system-allocated memory. Perhaps Microsoft has not made these functions public. If Microsoft has not provided such an API, I can only presume that it was for an intentional and specific reason. Would providing such a hook into the system prose a significant threat to system security? Situation Report Although knowing whether a memory pointer is valid could be useful in many scenarios, this is my particular situation: I am writing a driver for a new piece of hardware that is to replace an existing piece of hardware that connects to the PC via USB. My mandate is to write the new driver such that calls to the existing API for the current driver will continue to work in the PC applications in which it is used. Thus the only required changes to existing applications is to load the appropriate driver DLL(s) at startup. The problem here is that the existing driver uses a callback to send received serial messages to the application; a pointer to allocated memory containing the message is passed from the driver to the application via the callback. It is then the responsibility of the application to call another driver API to free the memory by passing back the same pointer from the application to the driver. In this scenario the second API has no way to determine if the application has actually passed back a pointer to valid memory.

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• How to search in this activerecord example?

  - by Horace Ho

  Two models: Invoice :invoice_num string :date datetime . . :disclaimer_num integer (foreign key) Disclaimer :disclaimer_num integer :version integer :body text For each disclaimer there are multiple versions and will be kept in database. This is how I write the search (simplified): scope = Invoice.scoped({ :joins => [:disclaimer] }) scope = scope.scoped :conditions => ["Invoice.invoice_num = ?", "#{params[:num]}"] scope = scope.scoped :conditions => ["Disclaimer.body LIKE ?", "%#{params[:text]}%"] However, the above search will search again all versions of the disclaimer. How can I limit the search to only the last disclaimer (i.e. the version integer is the maximum). Please note: Invoice does not keep the version number. New disclaimers will be added to disclaimer table and keep old versions.

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