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• Writing different structs to a file in C++? [on hold]

  - by user58053

  I need a way to write structures of three different kinds to a binary file, which later has to be searched. (As in, for example, struct A has two fields, an int and a char; struct B has int and a long; I need to output all structures whose int equals the one given from keyboard). I understand how to write structs of the same kind to a file and how to search them, but here I am just lost, best thing I came up with is declaring a struct containing all possibly needed fields and leaving the ones I don't need empty, but it really feels wrong, there HAS to be a better way to do that. I've read about binary files and could not find anything relevant, most examples and tutorials deal with writing one data type. Could anyone point me in the right direction? EDIT: I am looking for what @Jerry_coffin called database mode, and will probably use one of the existing database systems for that, best way to go, probably. Thank you everybody for the suggestions

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• Initializing an array after declaration

  - by robUK

  Hello, gcc 4.4.3 c89 I have the following code as a sample of what I am trying to do. I don't know the actual size of the array, until I enter the function. However, I don't think I can set the array size after I have declared it. I need it global as some other functions will need to access the device names. Many thanks for any suggestions, /* global */ char *devices_names[]; void fill_devices(size_t num_devices) { devices_names[num_devices]; /* start filling */ }

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• Pointer aliasing- in C++0x

  - by DeadMG

  I'm thinking about (just as an idea) disjointed pointer aliasing in C++0x. I was thinking about seeing if it could be implemented similarly to const correctness- that is, enforced by the compiler. What would be the requirements for such a thing? As this is more of a thought experiment, I'm perfectly happy to look at solutions that destroy legacy code or redefine half the language and that kind of thing. What I'd really rather not do is have, say, restrict from C99 where the programmer just promises it. It should be enforced.

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• why nResult != nConvertedLen,when use CComBSTR;

  - by hxboxy

  CComBSTR wsData = (char*)pvData; when constuct CComBSTR,call A2WBSTR,but sometimes nResult != nConvertedLen,just 1/20. why? inline BSTR A2WBSTR(_In_opt_ LPCSTR lp, int nLen = -1) { if (lp == NULL || nLen == 0) return NULL; USES_CONVERSION_EX; BSTR str = NULL; #pragma warning(push) #pragma warning(disable: 6385) int nConvertedLen = MultiByteToWideChar(_acp_ex, 0, lp, nLen, NULL, NULL); #pragma warning(pop) int nAllocLen = nConvertedLen; if (nLen == -1) nAllocLen -= 1; // Don't allocate terminating '\0' str = ::SysAllocStringLen(NULL, nAllocLen); if (str != NULL) { int nResult; nResult = MultiByteToWideChar(_acp_ex, 0, lp, nLen, str, nConvertedLen); ATLASSERT(nResult == nConvertedLen); if(nResult != nConvertedLen) { SysFreeString(str); return NULL; } } return str; }

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• Question about r-value in C++0x

  - by Goofy

  Rvalues IMHO are great improvement in C++, but at the beginning the're seems quite. Please look at code below: #include <string> std::string && foo (void) { std::string message ("Hello!"); return std::move (message); } void bar (const std::string &message2) { if (message == "Bye Bye!") return; } int main () { bar (foo ()); } Reference message2 is last owner of original message object returned by foo(), right?

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• an error within context

  - by helloWorld

  can somebody please explain my mistake, I have this class: class Account{ private: string strLastName; string strFirstName; int nID; int nLines; double lastBill; public: Account(string firstName, string lastName, int id); friend string printAccount(string firstName, string lastName, int id, int lines, double lastBill); } but when I call it: string reportAccounts() const { string report(printAccountsHeader()); for(list<Account>::const_iterator i = listOfAccounts.begin(); i != listOfAccounts.end(); ++i){ report += printAccount(i->strFirstName, i->strLastName, i->nID, i->nLines, i->lastBill);; } return report; } I receive error within context, can somebody explain why? thanks in advance

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• C++: Delete a struct?

  - by Rosarch

  I have a struct that contains pointers: struct foo { char* f; int* d; wchar* m; } I have a vector of shared pointers to these structs: vector<shared_ptr<foo>> vec; vec is allocated on the stack. When it passes out of scope at the end of the method, its destructor will be called. (Right?) That will in turn call the destructor of each element in the vector. (Right?) Does calling delete foo delete just the pointers such as foo.f, or does it actually free the memory from the heap?

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• An array of structures in C...

  - by 00010000

  For the life of me I can't figure out the proper syntax for creating an array of structures in C. I tried this: struct foo { int x; int y; } foo[][] = { { { 1, 2 }, { 4, 5 }, { -1, -1 } }, { { 55, 44 } { 100, 200 }, } }; So for example foo[1][0].x == 100, foo[0][1].y == 5, etc. But GCC spits out a lot of errors. If anyone could provide the proper syntax that'd be great. EDIT: Okay, I tried this: struct foo { const char *x; int y; }; struct foo bar[2][] = { { { "A", 1 }, { "B", 2 }, { NULL, -1 }, }, { { "AA", 11 }, { "BB", 22 }, { NULL, -1 }, }, { { "ZZ", 11 }, { "YY", 22 }, { NULL, -1 }, }, { { "XX", 11 }, { "UU", 22 }, { NULL, -1 }, }, }; But GCC gives me "elements of array bar have incomplete type" and "excess elements in array initializer".

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• what is the reason i am getting out put is 111?

  - by kam

  Hi, #include "stdafx.h" #include<iostream.h> template<class T> class Sample { public: Sample(); static int i; }; template<class T> int Sample<T>::i = 0; template<class T> Sample<T>::Sample() { i++; cout<<i; } void main() { Sample<int>s1; Sample<float>s2; Sample<char>s3; } output: 111 what is the reason i am getting out put is 111?

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• Row for each hour even if there is no record

  - by peku33

  I've got a trouble with creating mysql Query. My PHP script executes this query on each run: INSERT INTO Executes SET UserIp='%s' (%s is user IP) Executes table is: ExecuteId UNSIGNED BIGINT AI PRIMARY Date TIMESTAMP DEFAULT CURRENT_TIMESTAMP INDEX UserIp CHAR(24) ... | Some Columns I want to retrive number of Executes in each hour. The most obvious solution would be: SELECT COUNT(*) as ExecutesNum, DATE(Date) as D, HOUR(Date) as H GROUP BY D, H And it works, BUT it does not create rows for hours where there were no executes. What should I modify to get result like: 1 | 2012-09-01 | 14 **0 | 2012-09-01 | 15** 11 | 2012-09-01 | 16 1 | 2012-09-01 | 17

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• how to specify a pointer to an overloaded function?

  - by davka

  I want to pass an overloaded function to the std::for_each() algorithm. e.g.: void f(char c); void f(int i); std::string s("example"); std::for_each(s.begin(), s.end(), f); I'd expect the compiler to resolve f() by the iterator type. Apparently, it (gcc 4.1.2) doesn't do it. So, how can I specify which f() I want? thanks a lot

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• How to scramble string C#?

  - by a_Elnajjar

  I write the code to scramble word I am create simple game jumble string jumble = theWord; int length = jumble.Count(); for (int i = 0; i < length; ++i) { int index1 = (rand.Next() % length); int index2 = (rand.Next() % length); char temp =jumble[index1]; jumble = jumble.Replace(jumble[index1], jumble[index2]); jumble = jumble.Replace(jumble[index1], temp); }

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• Sending some byte at time

  - by user1417815

  I'm trying to figure out way to send some amount of text from the string ech time until it reach the end of the string, example: const char* the_string = "hello world, i'm happy to meet you all. Let be friends or maybe more, but nothing less" Output: hello world Output: , i'm happy to meet you all. Output: Let be friends or maybe more Output: , but nothing less stop: no more bytes to send. the problem i have searched google, but didn't understand the examples, i spent 4 days trying find a good way, also that sendt 5 bytes at time, but in case there is less, then send them until you are at the end of the string. please help me out guys, i will accept a C or C++ way, as long it works and well explained.

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• creating new array according to input

  - by gcc

  int *arrays[20],j,a=0; /*int num_arrays;*/ char *tutar[200]; int /*fe*/i=0,n,temp; do{ tutar[i]=malloc(sizeof(int)); scanf("%s",tutar[i]); temp=*tutar[i]; ++i; } while(temp!='x'); int *arrays[20],j,a=0; n=i; j=1; for(i=1;i if(atoi(tutar[i])=='n') { ++j; arrays[j]=malloc(sizeof(int)); a=0; } arrays[j][a]=*(int *)tutar[i]; if(atoi(tutar[i])=='x') break; } input: 1 2 3 4 n 14 23 39 n 98 100 x output: arrays[1]:2 3 4 arrays[2]:14 23 39 arrays[3]:98 100 //i wanna output like that but my code didnt give me output like that //can anyone fix my code or (explain where is my error)

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• I make this for balancing paranthesis of equation but i think it is wrong check and correct it

  - by muhammadlodhi

  int main(){ char i,input[30],close,open; for(i=0;i<='.';i++){ printf("enter equation"); scanf("%c",input[i]); if(input[i]=='(') input++; input[i]=open; else if(input[i]==')') input[i]--; input[i]=close; else if(open[i]==close[i]) { printf("paranthesis are balance"); } else printf("paranthesis are not balance"); } getch(); return 0; }

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• Why does the Win32-API have so many custom types?

  - by sub

  I'm new to the Win32 API and the many new types begin to confuse me. Some functions take 1-2 ints and 3 UINTS as arguments. Why can't they just use ints? What are UINTS? Then, there are those other types: DWORD LPCWSTR LPBOOL Again, I think the "primitive" C types would be enough - why introduce 100 new types? This one was a pain: WCHAR* I had to iterate through it and push_back every character to an std::string as there wasn't another way to convert it to one. Horrible. Why WCHAR? Why reinvent the wheel? They could have just used char* instead, or?

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• Obtain container type from (its) iterator type in C++ (STL)

  - by KRao

  It is easy given a container to get the associated iterators, example: std::vector<double>::iterator i; //An iterator to a std::vector<double> I was wondering if it is possible, given an iterator type, to deduce the type of the "corresponding container" (here I am assuming that for each container there is one and only one (non-const) iterator). More precisely, I would like a template metafunction that works with all STL containers (without having to specialize it manually for each single container) such that, for example: ContainerOf< std::vector<double>::iterator >::type evaluates to std::vector<double> Is it possible? If not, why? Thank you in advance for any help!

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• [C++] Simple inheritance question

  - by xbonez

  I was going over some sample questions for an upcoming test, and this question is totally confusing me. Any help would be appreciated. Consider the following code: class GraduateStudent : public Student { ... }; If the word "public" is omitted, GraduateStudent uses private inheritance, which means which of the following? GraduateStudent objects may not use methods of Student. GraduateStudent does not have access to private objects of Student. No method of GraduateStudent may call a method of Student. Only const methods of GraduateStudent can call methods of Student.

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• Gmock setting out parameter

  - by user1135541

  Have a gmock method, and during test, need to set the out parameter to variable address. So that the out parameter of dequeue, which is data points to variable ch; MOCK_METHOD1(dequeue, void(void* data)); char ch = 'm'; void* a = (void*)&ch; EXPECT_CALL(FQO, dequeue(_)) .WillOnce(/*here I need to set argument to a*/); I tried to figure out side effects: https://code.google.com/p/googlemock/wiki/V1_7_CheatSheet#Side_Effects but keep getting an error.

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• debug assertion fail

  - by Kolt

  I have a program that runs correctly if I start it manually. However, if I try to add a registry key to start it automatically during startup, I get this error: Debug assertion failed (str!=null) fprintf.c line:55 I tried to add Sleep(20000) before anything hapens, but same error. here`s the code: main() { FILE* filetowrite; filetowrite = fopen("textfile.txt", "a+"); writefunction(filetowrite); } int writefunction(FILE* filetowrite) { fprintf(filetowrite, "%s", "\n\n"); ... } I also tried with passing filename as char* and opening it in wrtiefunction(), but same error.

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• How does make_pair know the types of its args?

  - by bobobobo

  The definition for make_pair in the MSVC++ "utility" header is: template<class _Ty1, class _Ty2> inline pair<_Ty1, _Ty2> make_pair(_Ty1 _Val1, _Ty2 _Val2) { // return pair composed from arguments return (pair<_Ty1, _Ty2>(_Val1, _Val2)); } I use make_pair all the time though without putting the argument types in angle brackets: map<string,int> theMap ; theMap.insert( make_pair( "string", 5 ) ) ; Shouldn't I have to tell make_pair that the first argument is std::string and not char* ? How does it know?

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• Is there a method to retrieve the file name of a class?

  - by Dran Dane

  Hello Is there a method to retrieve the file name of a class? Specifically I would like to create a static method (CreateLink) in a base class (BasePage) to automatically return the path and filename of the page called. I code in .C# ASP.NET private const string TEMPLATE = "~/One.aspx"; public static HyperLink CreateLink() { HyperLink link = new HyperLink(); link.Text = "Click here"; link.NavigateUrl = String.Format(TEMPLATE); return link; } Is it possible to avoid the use of TEMPLATE hardcoded variable? Is it possible to retrieve the One.aspx path from file name and location?

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• How to do hex8 encoding in c?

  - by Tech163

  I am trying to encode a string in hex8 using c. The script I have right now is: int hex8 (char str) { str = printf("%x", str); if(strlen(str) == 1) { return printf("%s", "0", str); } else { return str; } } In this function, I will need to add a 0 ahead of the string if the length is less than 1. I don't know why I'm getting: passing argument 1 of 'strlen' makes pointer from integer without a cast Does anyone know why?

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• c language:make fgets to keep taking input until I press enter twice?

  - by wello horld

  hi I would like to ask how I would modify this code for the question: (It only accepts one input then prints it out. I want it to keep going until I hit enter (\n) twice. #include <stdio.h> #define MAXLENGTH 1000 int main(void) { char string[MAXLENGTH]; fgets(string, MAXLENGTH, stdin ); printf("%s\n", string); return 0; } I'm confused at the fgets(string, MAXLENGTH, stdin ); line, what does stdin mean/do?

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• [VC++ 2010] Stack around the variable 'xyz' was corrupted.

  - by tirolerhut

  hi, I'm trying to get some simple piece of code I found on a website to work in VC++ 2010 on windows vista 64: #include "stdafx.h" #include <windows.h> int _tmain(int argc, _TCHAR* argv[]) { DWORD dResult; BOOL result; char oldWallPaper[MAX_PATH]; result = SystemParametersInfo(SPI_GETDESKWALLPAPER, sizeof(oldWallPaper)-1, oldWallPaper, 0); fprintf(stderr, "Current desktop background is %s\n", oldWallPaper); return 0; } it does compile, but when I run it, I always get this error: Run-Time Check Failure #2 - Stack around the variable 'oldWallPaper' was corrupted. I'm not sure what is going wrong, but I noticed, that the value of oldWallPaper looks something like "C\0\:\0\0U\0s\0e\0r\0s[...]" -- I'm wondering where all the \0s come from. A friend of mine compiled it on windows xp 32 (also VC++ 2010) and is able to run it without problems any clues/hints/opinions? thanks

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