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• Boost.MultiIndex: How to make an effective set intersection?

  - by Arman

  Hello, assume that we have a data1 and data2. How can I intersect them with std::set_intersect()? struct pID { int ID; unsigned int IDf;// postition in the file pID(int id,const unsigned int idf):ID(id),IDf(idf){} bool operator<(const pID& p)const { return ID<p.ID;} }; struct ID{}; struct IDf{}; typedef multi_index_container< pID, indexed_by< ordered_unique< tag<IDf>, BOOST_MULTI_INDEX_MEMBER(pID,unsigned int,IDf)>, ordered_non_unique< tag<ID>,BOOST_MULTI_INDEX_MEMBER(pID,int,ID)> > > pID_set; ID_set data1, data2; Load(data1); Load(data2); pID_set::index<ID>::type& L1_ID_index=L1.data.get<ID>(); pID_set::index<ID>::type& L2_ID_index=L2.data.get<ID>(); // How do I use set_intersect? Kind regards, Arman.

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• Linux Kernel programming: trying to get vm_area_struct->vm_start crashes kernel

  - by confusedKid

  Hi, this is for an assignment at school, where I need to determine the size of the processes on the system using a system call. My code is as follows: ... struct task_struct *p; struct vm_area_struct *v; struct mm_struct *m; read_lock(&tasklist_lock); for_each_process(p) { printk("%ld\n", p->pid); m = p->mm; v = m->mmap; long start = v->vm_start; printk("vm_start is %ld\n", start); } read_unlock(&tasklist_lock); ... When I run a user level program that calls this system call, the output that I get is: 1 vm_start is 134512640 2 EIP: 0073:[<0806e352] CPU: 0 Not tainted ESP: 007b:0f7ecf04 EFLAGS: 00010246 Not tainted EAX: 00000000 EBX: 0fc587c0 ECX: 081fbb58 EDX: 00000000 ESI: bf88efe0 EDI: 0f482284 EBP: 0f7ecf10 DS: 007b ES: 007b 081f9bc0: [<08069ae8] show_regs+0xb4/0xb9 081f9bec: [<080587ac] segv+0x225/0x23d 081f9c8c: [<08058582] segv_handler+0x4f/0x54 081f9cac: [<08067453] sig_handler_common_skas+0xb7/0xd4 081f9cd4: [<08064748] sig_handler+0x34/0x44 081f9cec: [<080648b5] handle_signal+0x4c/0x7a 081f9d0c: [<08066227] hard_handler+0xf/0x14 081f9d1c: [<00776420] 0x776420 Kernel panic - not syncing: Kernel mode fault at addr 0x0, ip 0x806e352 EIP: 0073:[<400ea0f2] CPU: 0 Not tainted ESP: 007b:bf88ef9c EFLAGS: 00000246 Not tainted EAX: ffffffda EBX: 00000000 ECX: bf88efc8 EDX: 080483c8 ESI: 00000000 EDI: bf88efe0 EBP: bf88f038 DS: 007b ES: 007b 081f9b28: [<08069ae8] show_regs+0xb4/0xb9 081f9b54: [<08058a1a] panic_exit+0x25/0x3f 081f9b68: [<08084f54] notifier_call_chain+0x21/0x46 081f9b88: [<08084fef] __atomic_notifier_call_chain+0x17/0x19 081f9ba4: [<08085006] atomic_notifier_call_chain+0x15/0x17 081f9bc0: [<0807039a] panic+0x52/0xd8 081f9be0: [<080587ba] segv+0x233/0x23d 081f9c8c: [<08058582] segv_handler+0x4f/0x54 081f9cac: [<08067453] sig_handler_common_skas+0xb7/0xd4 081f9cd4: [<08064748] sig_handler+0x34/0x44 081f9cec: [<080648b5] handle_signal+0x4c/0x7a 081f9d0c: [<08066227] hard_handler+0xf/0x14 081f9d1c: [<00776420] 0x776420 The first process (pid = 1) gave me the vm_start without any problems, but when I try to access the second process, the kernel crashes. Can anyone tell me what's wrong, and maybe how to fix it as well? Thanks a lot! (sorry for the bad formatting....) edit: This is done in a Fedora 2.6 core in an uml environment.

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• Chunked responses in libevent2

  - by Sri

  Hi I am trying to do a chunked response (of large files) in libevent this way:: evhttp_send_reply_start(request, HTTP_OK, "OK"); int fd = open("filename", O_RDONLY); size_t fileSize = <get_file_size>; struct evbuffer *databuff = NULL; for (off_t offset = 0;offset < fileSize;) { databuff = evbuffer_new(); size_t bytesLeft = fileSize - offset; size_t bytesToRead = bytesLeft > MAX_READ_SIZE ? MAX_READ_SIZE : bytesLeft; evbuffer_add_file(databuff, fd, offset, bytesToRead); offset += bytesToRead; evhttp_send_reply_chunk(request, databuff); // send it evbuffer_free(databuff); // destroy it } evhttp_send_reply_end(request); fclose(fptr); Problem is with this I have a feeling the add_file is asynchronous so the 3rd or so evhttp_send_reply_chunk gives me an error (or something similar): [warn] evhttp_send_chain Closed(45): Bad file descriptor I set MAX_READ_SIZE to be 8 to actually test out chunked transfer encoding. I noticed there was a evhttp_request_set_chunked_cb (struct evhttp_request *, void(*cb)(struct evhttp_request *, void *)) method I could use but could not find any examples on how to use. For instance, how could I pass an argument to the callback? The argument seems to be the same argument that was passed to the request handler which is not what I want, because I want to create an object that holds the file descriptor and the file offset I am sending out. Appreciate all help. Thanks in advance Sri

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• how to use gettimeofday() or something equivalent with Visual Studio C++ 2008?

  - by make

  Hi, Could someone please help me to use gettimeofday() function with Visual Studio C++ 2008 on Windows XP? here is a code that I found somewhere on the net: #include < time.h > #include <windows.h> #if defined(_MSC_VER) || defined(_MSC_EXTENSIONS) #define DELTA_EPOCH_IN_MICROSECS 11644473600000000Ui64 #else #define DELTA_EPOCH_IN_MICROSECS 11644473600000000ULL #endif struct timezone { int tz_minuteswest; /* minutes W of Greenwich */ int tz_dsttime; /* type of dst correction */ }; int gettimeofday(struct timeval *tv, struct timezone *tz) { FILETIME ft; unsigned __int64 tmpres = 0; static int tzflag; if (NULL != tv) { GetSystemTimeAsFileTime(&ft); tmpres |= ft.dwHighDateTime; tmpres <<= 32; tmpres |= ft.dwLowDateTime; /*converting file time to unix epoch*/ tmpres -= DELTA_EPOCH_IN_MICROSECS; tmpres /= 10; /*convert into microseconds*/ tv->tv_sec = (long)(tmpres / 1000000UL); tv->tv_usec = (long)(tmpres % 1000000UL); } if (NULL != tz) { if (!tzflag) { _tzset(); tzflag++; } tz->tz_minuteswest = _timezone / 60; tz->tz_dsttime = _daylight; } return 0; } ... // call gettimeofday() gettimeofday(&tv, &tz); tm = localtime(&tv.tv_sec); Last yesr when I tested this code VC++6, it works fine. But now when I use VC++ 2008, I am getting error of exception handling. So is there any idea on how to use gettimeofday or something equivalent? Thanks for your reply and any help would be very appreciated:

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• Go XML Unmarshal example doesn't compile

  - by marketer

  The Xml example in the go docs is broken. Does anyone know how to make it work? When I compile it, the result is: xmlexample.go:34: cannot use "name" (type string) as type xml.Name in field value xmlexample.go:34: cannot use nil as type string in field value xmlexample.go:34: too few values in struct initializer Here is the relevant code: package main import ( "bytes" "xml" ) type Email struct { Where string "attr"; Addr string; } type Result struct { XMLName xml.Name "result"; Name string; Phone string; Email []Email; } var buf = bytes.NewBufferString ( ` <result> <email where="home"> <addr>[email protected]</addr> </email> <email where='work'> <addr>[email protected]</addr> </email> <name>Grace R. Emlin</name> <address>123 Main Street</address> </result>`) func main() { var result = Result{ "name", "phone", nil } xml.Unmarshal ( buf , &result ) println ( result.Name ) }

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• Getting Vars to bind properly across multiple files

  - by Alex Baranosky

  I am just learning Clojure and am having trouble moving my code into different files. I keep detting this error from the appnrunner.clj - Exception in thread "main" java.lang.Exception: Unable to resolve symbol: -run-application in this context It seems to be finding the namespaces fine, but then not seeing the Vars as being bound... Any idea how to fix this? Here's my code: APPLICATION RUNNER - (ns src/apprunner (:use src/functions)) (def input-files [(resource-path "a.txt") (resource-path "b.txt") (resource-path "c.txt")]) (def output-file (resource-path "output.txt")) (defn run-application [] (sort-files input-files output-file)) (-run-application) APPLICATION FUNCTIONS - (ns src/functions (:use clojure.contrib.duck-streams)) (defn flatten [x] (let [s? #(instance? clojure.lang.Sequential %)] (filter (complement s?) (tree-seq s? seq x)))) (defn resource-path [file] (str "C:/Users/Alex and Paula/Documents/SoftwareProjects/MyClojureApp/resources/" file)) (defn split2 [str delim] (seq (.split str delim))) (defstruct person :first-name :last-name) (defn read-file-content [file] (apply str (interpose "\n" (read-lines file)))) (defn person-from-line [line] (let [sections (split2 line " ")] (struct person (first sections) (second sections)))) (defn formatted-for-display [person] (str (:first-name person) (.toUpperCase " ") (:last-name person))) (defn sort-by-keys [struct-map keys] (sort-by #(vec (map % [keys])) struct-map)) (defn formatted-output [persons output-number] (let [heading (str "Output #" output-number "\n") sorted-persons-for-output (apply str (interpose "\n" (map formatted-for-display (sort-by-keys persons (:first-name :last-name)))))] (str heading sorted-persons-for-output))) (defn read-persons-from [file] (let [lines (read-lines file)] (map person-from-line lines))) (defn write-persons-to [file persons] (dotimes [i 3] (append-spit file (formatted-output persons (+ 1 i))))) (defn sort-files [input-files output-file] (let [persons (flatten (map read-persons-from input-files))] (write-persons-to output-file persons)))

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• Questions on usages of sizeof

  - by Appu

  Question 1 I have a struct like, struct foo { int a; char c; }; When I say sizeof(foo), i am getting 8 on my machine. As per my understanding, 4 bytes for int, 1 byte for char and 3 bytes for padding. Is that correct? Given a struct like the above, how will I find out how many bytes will be added as padding? Question 2 I am aware that sizeof can be used to calculate the size of an array. Mostly I have seen the usage like (foos is an array of foo) sizeof(foos)/sizeof(*foos) But I found that the following will also give same result. sizeof(foos) / sizeof(foo) Is there any difference in these two? Which one is preffered? Question 3 Consider the following statement. foo foos[] = {10,20,30}; When I do sizeof(foos) / sizeof(*foos), it gives 2. But the array has 3 elements. If I change the statement to foo foos[] = {{10},{20},{30}}; it gives correct result 3. Why is this happening? Any thoughts..

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• How do I pass an array of structs (containing std:string or BSTR) from ATL to C#. SafeArray? Varian

  - by Andrew

  Hi, I have an ATL COM object that I am using from C#. The interface currently looks like: interface ICHASCom : IDispatch{ [id(1), helpstring("method Start")] HRESULT Start([in] BSTR name, [out,retval] VARIANT_BOOL* result); ... [id(4), helpstring("method GetCount")] HRESULT GetCount([out,retval] LONG* numPorts); ... [id(7), helpstring("method EnableLogging")] HRESULT EnableLogging([in] VARIANT_BOOL enableLogging); }; That is, it's a very simple interface. I also have some events that I send back too. Now, I would like to add something to the interface. In the ATL I have some results, which are currently structs and look like struct REPORT_LINE { string creationDate; string Id; string summary; }; All the members of the struct are std::string. I have an array of these that I need to get back to the C#. What's the best way to do this? I suspect someone is going to say, "hey, you can't just send std::string over COM like that. If so, fine, but what's the best way to modidfy the struct? Change the std::string to BSTR? And then how do I, 1) Set up the IDL to pass an array of structs (structs with BSTR or std::string) 2) If I must use SAFEARRAYS, how do I fill the SAFEARRAYS with the structs. I'm not familiar with COM except for use with simple types. Thanks, Dave

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• Overloading the QDataStream << and >> operators for a user-defined type

  - by Alex Wood

  I have a an object I'd like to be able to read and write to/from a QDataStream. The header is as follows: class Compound { public: Compound(QString, QPixmap*, Ui::MainWindow*); void saveCurrentInfo(); void restoreSavedInfo(QGraphicsScene*); void setImage(QPixmap*); QString getName(); private: QString name, homeNotes, addNotes, expText; Ui::MainWindow *gui; QPixmap *image; struct NMRdata { QString hnmrText, cnmrText, hn_nmrText, hn_nmrNucl, notes; int hnmrFreqIndex, cnmrFreqIndex, hn_nmrFreqIndex, hnmrSolvIndex, cnmrSolvIndex, hn_nmrSolvIndex; }*nmr_data; struct IRdata { QString uvConc, lowResMethod, irText, uvText, lowResText, highResText, highResCalc, highResFnd, highResFrmla, notes; int irSolvIndex, uvSolvIndex; }*ir_data; struct PhysicalData { QString mpEdit, bpEdit, mpParensEdit, bpParensEdit, rfEdit, phyText, optAlpha, optConc, elemText, elemFrmla, notes; int phySolvIndex, optSolvIndex; }*physical_data; }; For all intensive purposes, the class just serves as an abstraction for a handful of QStrings and a QPixmap. Ideally, I would be able to write a QList to a QDataStream but I'm not exactly sure how to go about doing this. If operator overloading is a suitable solution, would writing code like friend QDataStream& operator << (QDataStream&,Compound) { ... } be a potential solution? I'm very open to suggestions! Please let me know if any further clarification is needed.

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• Problem calling std::max

  - by Eric

  I compiled my bison-generated files in Visual Studio and got these errors: ...\position.hh(83): error C2589: '(' : illegal token on right side of '::' ...\position.hh(83): error C2059: syntax error : '::' ...\position.hh(83): error C2589: '(' : illegal token on right side of '::' ...\position.hh(83): error C2059: syntax error : '::' The corresponding code is: inline void columns (int count = 1) { column = std::max (1u, column + count); } I think the problem is with std::max; if I change std::max to equivalent code then there is no problem anymore, but is there a better solution instead of changing the generated code? Here is the bison file I wrote: // // bison.yy // %skeleton "lalr1.cc" %require "2.4.2" %defines %define parser_class_name "cmd_parser" %locations %debug %error-verbose %code requires { class ParserDriver; } %parse-param { ParserDriver& driver } %lex-param { ParserDriver& driver } %union { struct ast *a; double d; struct symbol *s; struct symlist *sl; int fn; } %code { #include "helper_func.h" #include "ParserDriver.h" std::string error_msg = ""; } %token <d> NUMBER %token <s> NAME %token <fn> FUNC %token EOL %token IF THEN ELSE WHILE DO LET %token SYM_TABLE_OVERFLOW %token UNKNOWN_CHARACTER %nonassoc <fn> CMP %right '=' %left '+' '-' %left '*' '/' %nonassoc '|' UMINUS %type <a> exp stmt list explist %type <sl> symlist %{ extern int yylex(yy::cmd_parser::semantic_type *yylval, yy::cmd_parser::location_type* yylloc); %} %start calclist %% ... grammar rules ...

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• Good hash function for a 2d index

  - by rlbond

  I have a struct called Point. Point is pretty simple: struct Point { Row row; Column column; // some other code for addition and subtraction of points is there too } Row and Column are basically glorified ints, but I got sick of accidentally transposing the input arguments to functions and gave them each a wrapper class. Right now I use a set of points, but repeated lookups are really slowing things down. I want to switch to an unordered_set. So, I want to have an unordered_set of Points. Typically this set might contain, for example, every point on a 80x24 terminal = 1920 points. I need a good hash function. I just came up with the following: struct PointHash : public std::unary_function<Point, std::size_t> { result_type operator()(const argument_type& val) const { return val.row.value() * 1000 + val.col.value(); } }; However, I'm not sure that this is really a good hash function. I wanted something fast, since I need to do many lookups very quickly. Is there a better hash function I can use, or is this OK?

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• Wrapping FUSE from Go

  - by Matt Joiner

  I'm playing around with wrapping FUSE with Go. However I've come stuck with how to deal with struct fuse_operations. I can't seem to expose the operations struct by declaring type Operations C.struct_fuse_operations as the members are lower case, and my pure-Go sources would have to use C-hackery to set the members anyway. My first error in this case is "can't set getattr" in what looks to be the Go equivalent of a default copy constructor. My next attempt is to expose an interface that expects GetAttr, ReadLink etc, and then generate C.struct_fuse_operations and bind the function pointers to closures that call the given interface. This is what I've got (explanation continues after code): package fuse // #include <fuse.h> // #include <stdlib.h> import "C" import ( //"fmt" "os" "unsafe" ) type Operations interface { GetAttr(string, *os.FileInfo) int } func Main(args []string, ops Operations) int { argv := make([]*C.char, len(args) + 1) for i, s := range args { p := C.CString(s) defer C.free(unsafe.Pointer(p)) argv[i] = p } cop := new(C.struct_fuse_operations) cop.getattr = func(*C.char, *C.struct_stat) int {} argc := C.int(len(args)) return int(C.fuse_main_real(argc, &argv[0], cop, C.size_t(unsafe.Sizeof(cop)), nil)) } package main import ( "fmt" "fuse" "os" ) type CpfsOps struct { a int } func (me *CpfsOps) GetAttr(string, *os.FileInfo) int { return -1; } func main() { fmt.Println(os.Args) ops := &CpfsOps{} fmt.Println("fuse main returned", fuse.Main(os.Args, ops)) } This gives the following error: fuse.go:21[fuse.cgo1.go:23]: cannot use func literal (type func(*_Ctype_char, *_Ctype_struct_stat) int) as type *[0]uint8 in assignment I'm not sure what to pass to these members of C.struct_fuse_operations, and I've seen mention in a few places it's not possible to call from C back into Go code. If it is possible, what should I do? How can I provide the "default" values for interface functions that acts as though the corresponding C.struct_fuse_operations member is set to NULL?

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• Disassembling with python - no easy solution?

  - by Abc4599

  Hi, I'm trying to create a python script that will disassemble a binary (a Windows exe to be precise) and analyze its code. I need the ability to take a certain buffer, and extract some sort of struct containing information about the instructions in it. I've worked with libdisasm in C before, and I found it's interface quite intuitive and comfortable. The problem is, its Python interface is available only through SWIG, and I can't get it to compile properly under Windows. At the availability aspect, diStorm provides a nice out-of-the-box interface, but it provides only the Mnemonic of each instruction, and not a binary struct with enumerations defining instruction type and what not. This is quite uncomfortable for my purpose, and will require a lot of what I see as spent time wrapping the interface to make it fit my needs. I've also looked at BeaEngine, which does in fact provide the output I need, a struct with binary info concerning each instruction, but its interface is really odd and counter-intuitive, and it crashes pretty much instantly when provided with wrong arguments. The CTypes sort of ultimate-death-to-your-python crashes. So, I'd be happy to hear about other solutions, which are a little less time consuming than messing around with djgcc or mingw to make SWIGed libdisasm, or writing an OOP wrapper for diStorm. If anyone has some guidance as to how to compile SWIGed libdisasm, or better yet, a compiled binary (pyd or dll+py), I'd love to hear/have it. :) Thanks ahead.

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• Linked list recursive reverse

  - by Phoenix

  I was looking at the code below from stanford library: void recursiveReverse(struct node** head_ref) { struct node* first; struct node* rest; /* empty list */ if (*head_ref == NULL) return; /* suppose first = {1, 2, 3}, rest = {2, 3} */ first = *head_ref; rest = first->next; /* List has only one node */ if (rest == NULL) return; /* put the first element on the end of the list */ recursiveReverse(&rest); first->next->next = first; /* tricky step -- see the diagram */ first->next = NULL; /* fix the head pointer */ *head_ref = rest; } What I don't understand is in the last recursive step for e.g if list is 1-2-3-4 Now for the last recursive step first will be 1 and rest will be 2. So if you set *head_ref = rest .. that makes the head of the list 2 ?? Can someone please explain how after reversing the head of the list becomes 4 ??

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• Persist changes in C

  - by Mohit Deshpande

  I am developing a database-like application that stores a a structure containing: struct Dictionary { char *key; char *value; struct Dictionary *next; }; As you can see, I am using a linked list to store information. But the problem begins when the user exits out of the program. I want the information to be stored somewhere. So I was thinking of storing the linked list in a permanent or temporary file using fopen, then, when the user starts the program, retrieve the linked list. Here is the method that prints the linked list to the console: void PrintList() { int count = 0; struct Dictionary *current; current = head; if (current == NULL) { printf("\nThe list is empty!"); return; } printf(" Key \t Value\n"); printf(" ======== \t ========\n"); while (current != NULL) { count++; printf("%d. %s \t %s\n", count, current->key, current->value); current = current->next; } } So I am thinking of modifying this method to print the information through fprintf instead of printf and then the program would just get the infomation from the file. Could someone help me on how I can read and write to this file? What kind of file should it be, temporary or regular? How should I format the file (like I was thinking of just having the key first, then the value, then a newline character)?

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• errors when using c++ bison ---- in the file position.hh

  - by Eric

  firstly I'm not good at English so forgive me. I compile my program with the bison generated files in visual studio and get these errors: ...\position.hh(83): error C2589: '(' : illegal token on right side of '::' ...\position.hh(83): error C2059: syntax error : '::' ...\position.hh(83): error C2589: '(' : illegal token on right side of '::' ...\position.hh(83): error C2059: syntax error : '::' and the corresponding code is: inline void columns (int count = 1) { column = std::max (1u, column + count); } I think the problem is with std::max. If I change std::max to equivalent code then there is problem anymore, but is there a better solution instead of changing the generated code? here is the *.yy file I wrote. // // bison.yy // %skeleton "lalr1.cc" %require "2.4.2" %defines %define parser_class_name "cmd_parser" %locations %debug %error-verbose %code requires { class ParserDriver; } %parse-param { ParserDriver& driver } %lex-param { ParserDriver& driver } %union { struct ast *a; double d; struct symbol *s; struct symlist *sl; int fn; } %code { #include "helper_func.h" #include "ParserDriver.h" std::string error_msg = ""; } %token <d> NUMBER %token <s> NAME %token <fn> FUNC %token EOL %token IF THEN ELSE WHILE DO LET %token SYM_TABLE_OVERFLOW %token UNKNOWN_CHARACTER %nonassoc <fn> CMP %right '=' %left '+' '-' %left '*' '/' %nonassoc '|' UMINUS %type <a> exp stmt list explist %type <sl> symlist %{ extern int yylex(yy::cmd_parser::semantic_type *yylval, yy::cmd_parser::location_type* yylloc); %} %start calclist %% ... grammar rules ...

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• OutOfMemoryException

  - by Andrew

  I have an application that is pretty memory hungry. It holds a large amount of data in some big arrays. I have recently been noticing the occasional OutOfMemoryException. These OutOfMemoryExceptions are occurring long before my application (ASP.Net) has used up the 800mb available to it. I have track the issue down to the area of code where the array is resized. The array contains a structure that is 74bytes in size. (I know that you shouldn't create struct's that are bigger than 16bytes), but this application is a port from a Vb6 application). I have tried changing the struct to a class and this appears to have fixed the problem for now. I think the reason that changing to a class solves the problem has to do with the fact that when using a struct and the array is resized, a segment of memory that is large enough to store the new array needs to be reserved (e.g. (currentArraySize + increaseBySize)*74) cannot be found. This leads to the OutOfMemoryException. This isn't the case with a class as each element of the array only needs 8bytes to store a pointer to the new object. Is my thinking correct here?

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• How to simulate inner exception in C++

  - by Siva Chandran

  Basically I want to simulate .NET Exception.InnerException in C++. I want to catch exception from bottom layer and wrap it with another exception and throw again to upper layer. The problem here is I don't know how to wrap the catched exception inside another exception. struct base_exception : public std::exception { std::exception& InnerException; base_exception() : InnerException(???) { } // <---- what to initialize with base_exception(std::exception& innerException) : InnerException(innerException) { } }; struct func1_exception : public base_exception { const char* what() const throw() { return "func1 exception"; } }; struct func2_exception : public base_exception { const char* what() const throw() { return "func2 exception"; } }; void func2() { throw func2_exception(); } void func1() { try { func2(); } catch(std::exception& e) { throw func2_exception(e); // <--- is this correct? will the temporary object will be alive? } } int main(void) { try { func1(); } catch(base_exception& e) { std::cout << "Got exception" << std::endl; std::cout << e.what(); std::cout << "InnerException" << std::endl; std::cout << e.InnerException.what(); // <---- how to make sure it has inner exception ? } } In the above code listing I am not sure how to initialize the "InnerException" member when there is no inner exception. Also I am not sure whether the temporary object that is thrown from func1 will survive even after func2 throw?

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• array of structs in C

  - by Hristo

  I'm trying to create an array of structs and also a pointer to that array. I don't know how large the array is going to be, so it should be dynamic. My struct would look something like this: typedef struct _stats_t { int hours[24]; int numPostsInHour; int days[7]; int numPostsInDay; int weeks[20]; int numPostsInWeek; int totNumLinesInPosts; int numPostsAnalyzed; } stats_t; ... and I need to have multiple of these structs for each file (unknown amount) that I will analyze. I'm not sure how to do this. I don't like the following approach because of the limit of the size of the array: # define MAX 10 typedef struct _stats_t { int hours[24]; int numPostsInHour; int days[7]; int numPostsInDay; int weeks[20]; int numPostsInWeek; int totNumLinesInPosts; int numPostsAnalyzed; } stats_t[MAX]; So how would I create this array? Also, would a pointer to this array would look something this? stats_t stats[]; stats_t *statsPtr = &stats[0]; Thanks, Hristo

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• stat() get group name is root

  - by mengmenger

  I have a file src.tar.gz whoes owner and group are named "src". When I run test.c compiled with name "test" (permission: -rwsr-xr-x owner:root group:staff) The way I run it: I am running it as group member under "src" group. But I run "test" as root since "test" permission is -rwsr-xr-x Question: Why did result come out like this? is the src.tar.gz group should be "src"? Output: Error: my group: src Error: src.tar.gz group is root test.c #include <stdio.h> #include <stdlib.h> #include <unistd.h> #include <string.h> #include <sys/types.h> #include <sys/stat.h> #include <grp.h> void main(int ac, char **args) { const char *ERR_MSG_FORMAT = "%s: %s %s.\n"; char *ptr_source_file = "src.tar.gz"; struct stat src_stat; gid_t src_gid, my_gid; int i = stat(ptr_source_file, &src_stat); my_gid = getgid(); struct group *cur_gr = getgrgid(my_gid); fprintf(stderr, ERR_MSG_FORMAT, "Error", "my group: ", cur_gr->gr_name); src_gid = src_stat.st_gid; struct group *src_gr = getgrgid(src_gid); fprintf(stderr, ERR_MSG_FORMAT, "Error","src.tar.gz group is ", src_gr->gr_name); }

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• CStdioFile Undeclared Identifier

  - by Eric Regnier

  I am unable to compile my code when using a CStdioFile type. I have included the afx.h header file but I am still receiving errors. What I am trying to do is write a cstring that contains an entire xml document to file. This cstring contains comments inside of it, but when I use other objects such as wofstream to write it to file, these comments are striped out for some reason. So that is why I am trying to write this to file using CStdioFile now. If anyone can help me out as to why I cannot compile my code using CStdioFile, or any other way to write a cstring that contains xml comments to file, please let me know! Below is my code using CStdioFile: CStdioFile xmlFile; xmlFile.Open( "c:\\test.txt", CFile::modeCreate | CFile::modeWrite | CFile::typeText ); xmlFile.WriteString( m_sData ); xmlFile.Close(); And my errors: error C2065: 'CStdioFile' : undeclared identifier error C2065: 'modeCreate' : undeclared identifier error C2065: 'modeWrite' : undeclared identifier error C2065: 'typeText' : undeclared identifier error C2065: 'xmlFile' : undeclared identifier error C2146: syntax error : missing ';' before identifier 'xmlFile' error C2228: left of '.Close' must have class/struct/union type type is ''unknown-type'' error C2228: left of '.Open' must have class/struct/union type type is ''unknown-type'' error C2228: left of '.WriteString' must have class/struct/union type type is ''unknown-type'' error C2653: 'CFile' : is not a class or namespace name error C2653: 'CFile' : is not a class or namespace name error C2653: 'CFile' : is not a class or namespace name error C3861: 'xmlFile': identifier not found, even with argument-dependent lookup error C3861: 'xmlFile': identifier not found, even with argument-dependent lookup error C3861: 'xmlFile': identifier not found, even with argument-dependent lookup

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• Copy vector of values to vector of pairs in one line

  - by Kirill V. Lyadvinsky

  I have the following types: struct X { int x; X( int val ) : x(val) {} }; struct X2 { int x2; X2() : x2() {} }; typedef std::pair<X, X2> pair_t; typedef std::vector<pair_t> pairs_vec_t; typedef std::vector<X> X_vec_t; I need to initialize instance of pairs_vec_t with values from X_vec_t. I use the following code and it works as expected: int main() { pairs_vec_t ps; X_vec_t xs; // this is not empty in the production code ps.reserve( xs.size() ); { // I want to change this block to one line code. struct get_pair { pair_t operator()( const X& value ) { return std::make_pair( value, X2() ); } }; std::transform( xs.begin(), xs.end(), back_inserter(ps), get_pair() ); } return 0; } What I'm trying to do is to reduce my copying block to one line with using boost::bind. This code is not working: for_each( xs.begin(), xs.end(), boost::bind( &pairs_vec_t::push_back, ps, boost::bind( &std::make_pair, _1, X2() ) ) ); I know why it is not working, but I want to know how to make it working without declaring extra functions and structs?

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• If the address of a function can not be resolved during deduction, is it SFINAE or a compiler error?

  - by Faisal Vali

  In C++0x SFINAE rules have been simplified such that any invalid expression or type that occurs in the "immediate context" of deduction does not result in a compiler error but rather in deduction failure (SFINAE). My question is this: If I take the address of an overloaded function and it can not be resolved, is that failure in the immediate-context of deduction? (i.e is it a hard error or SFINAE if it can not be resolved)? Here is some sample code: struct X { // template T* foo(T,T); // lets not over-complicate things for now void foo(char); void foo(int); }; template struct S { template struct size_map { typedef int type; }; // here is where we take the address of a possibly overloaded function template void f(T, typename size_map::type* = 0); void f(...); }; int main() { S s; // should this cause a compiler error because 'auto T = &X::foo' is invalid? s.f(3); } Gcc 4.5 states that this is a compiler error, and clang spits out an assertion violation. Here are some more related questions of interest: Does the FCD-C++0x clearly specify what should happen here? Are the compilers wrong in rejecting this code? Does the "immediate-context" of deduction need to be defined a little better? Thanks!

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• Pointer problem in C for char*

  - by egebilmuh

  Hi guys, i use pointer for holding name and research lab property. But when i print the existing Vertex ,when i print the vertex, i cant see so -called attributes properly. For example though real value of name is "lancelot" , i see it as wrong such as "asdasdasdasd" struct vertex { int value; char*name; char* researchLab; struct vertex *next; struct edge *list; }; void GRAPHinsertV(Graph G, int value,char*name,char*researchLab) { //create new Vertex. Vertex newV = malloc(sizeof newV); // set value of new variable to which belongs the person. newV->value = value; newV->name=name; newV->researchLab=researchLab; newV->next = G->head; newV->list = NULL; G->head = newV; G->V++; } /*** The method creates new person. **/ void createNewPerson(Graph G) { int id; char name[30]; char researchLab[30]; // get requeired variables. printf("Enter id of the person to be added.\n"); scanf("%d",&id); printf("Enter name of the person to be added.\n"); scanf("%s",name); printf("Enter researc lab of the person to be added\n"); scanf("%s",researchLab); // insert the people to the social network. GRAPHinsertV(G,id,name,researchLab); } void ListAllPeople(Graph G) { Vertex tmp; Edge list; for(tmp = G->head;tmp!=NULL;tmp=tmp->next) { fprintf(stdout,"V:%d\t%s\t%s\n",tmp->value,tmp->name,tmp->researchLab); } system("pause"); }

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• Simple dynamic memory allocation bug.

  - by M4design

  I'm sure you (pros) can identify the bug's' in my code, I also would appreciate any other comments on my code. BTW, the code crashes after I run it. #include <stdlib.h> #include <stdio.h> #include <stdbool.h> typedef struct { int x; int y; } Location; typedef struct { bool walkable; unsigned char walked; // number of times walked upon } Cell; typedef struct { char name[40]; // Name of maze Cell **grid; // 2D array of cells int rows; // Number of rows int cols; // Number of columns Location entrance; } Maze; Maze *maz_new() { int i = 0; Maze *mazPtr = (Maze *)malloc(sizeof (Maze)); if(!mazPtr) { puts("The memory couldn't be initilised, Press ENTER to exit"); getchar(); exit(-1); } else { // allocating memory for the grid mazPtr->grid = (Cell **) malloc((sizeof (Cell)) * (mazPtr->rows)); for(i = 0; i < mazPtr->rows; i++) mazPtr->grid[i] = (Cell *) malloc((sizeof (Cell)) * (mazPtr->cols)); } return mazPtr; } void maz_delete(Maze *maz) { int i = 0; if (maz != NULL) { for(i = 0; i < maz->rows; i++) free(maz->grid[i]); free(maz->grid); } } int main() { Maze *ptr = maz_new(); maz_delete(ptr); getchar(); return 0; } Thanks in advance.

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