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  • C++ Word-Number to int

    - by Andrew
    I'm developing a program that makes basic calculations using words instead of numbers. E.g. five + two would output seven. The program becomes more complex, taking input such as two_hundred_one + five_thousand_six (201 + 5006) Through operator overloading methods, I split each number and assign it to it's own array index. two would be [0], hundred is [1], and one is [2]. Then the array recycles for 5006. My problem is, to perform the actual calculation, I need to convert the words stored in the array to actual integers. I have const string arrays such as this as a library of the words: const string units[] = { "", "one", "two", "three", "four", "five", "six", "seven", "eight", "nine" }; const string teens[] = { "ten", "eleven", "twelve", "thirteen", "fourteen", "fifteen", "sixteen", "seventeen", "eighteen", "nineteen" }; const string tens[] = { "", "", "twenty", "thirty", "forty", "fifty", "sixty", "seventy", "eighty", "ninety" }; If my 'token' array has stored in it two hundred one in index 0, 1, and 2, I'm not sure what the best way to convert these to ints would involve.

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  • optimize output value using a class and public member

    - by wiso
    Suppose you have a function, and you call it a lot of times, every time the function return a big object. I've optimized the problem using a functor that return void, and store the returning value in a public member: #include <vector> const int N = 100; std::vector<double> fun(const std::vector<double> & v, const int n) { std::vector<double> output = v; output[n] *= output[n]; return output; } class F { public: F() : output(N) {}; std::vector<double> output; void operator()(const std::vector<double> & v, const int n) { output = v; output[n] *= n; } }; int main() { std::vector<double> start(N,10.); std::vector<double> end(N); double a; // first solution for (unsigned long int i = 0; i != 10000000; ++i) a = fun(start, 2)[3]; // second solution F f; for (unsigned long int i = 0; i != 10000000; ++i) { f(start, 2); a = f.output[3]; } } Yes, I can use inline or optimize in an other way this problem, but here I want to stress on this problem: with the functor I declare and construct the output variable output only one time, using the function I do that every time it is called. The second solution is two time faster than the first with g++ -O1 or g++ -O2. What do you think about it, is it an ugly optimization?

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  • C: reading file and populating struct

    - by deostroll
    Hi, I have a structure with the following definition: typedef struct myStruct{ int a; char* c; int f; } OBJECT; I am able to populate this object and write it to a file. However I am not able to read the char* c value in it...while trying to read it, it gives me a segmentation fault error. Is there anything wrong with my code: //writensave.c #include "mystruct.h" #include <stdio.h> #include <string.h> #define p(x) printf(x) int main() { p("Creating file to write...\n"); FILE* file = fopen("struct.dat", "w"); if(file == NULL) { printf("Error opening file\n"); return -1; } p("creating structure\n"); OBJECT* myObj = (OBJECT*)malloc(sizeof(OBJECT)); myObj->a = 20; myObj->f = 45; myObj->c = (char*)calloc(30, sizeof(char)); strcpy(myObj->c, "This is a test"); p("Writing object to file...\n"); fwrite(myObj, sizeof(OBJECT), 1, file); p("Close file\n"); fclose(file); p("End of program\n"); return 0; } Here is how I am trying to read it: //readnprint.c #include "mystruct.h" #include <stdio.h> #define p(x) printf(x) int main() { FILE* file = fopen("struct.dat", "r"); char* buffer; buffer = (char*) malloc(sizeof(OBJECT)); if(file == NULL) { p("Error opening file"); return -1; } fread((void *)buffer, sizeof(OBJECT), 1, file); OBJECT* obj = (OBJECT*)buffer; printf("obj->a = %d\nobj->f = %d \nobj->c = %s", obj->a, obj->f, obj->c); fclose(file); return 0; }

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  • Returning and printing string array index in C

    - by user1781966
    I've got a function that searches through a list of names and I'm trying to get the search function to return the index of the array back to the main function and print out the starting location of the name found. Everything I've tried up to this point either crashes the program or results in strange output. Here is my search function: #include<stdio.h> #include<conio.h> #include<string.h> #define MAX_NAMELENGTH 10 #define MAX_NAMES 5 void initialize(char names[MAX_NAMES][MAX_NAMELENGTH], int Number_entrys, int i); int search(char names[MAX_NAMES][MAX_NAMELENGTH], int Number_entrys); int main() { char names[MAX_NAMES][MAX_NAMELENGTH]; int i, Number_entrys,search_result,x; printf("How many names would you like to enter to the list?\n"); scanf("%d",&Number_entrys); initialize(names,Number_entrys,i); search_result= search(names,Number_entrys); if (search_result==-1){ printf("Found no names.\n"); }else { printf("%s",search_result); } getch(); return 0; } void initialize(char names[MAX_NAMES][MAX_NAMELENGTH],int Number_entrys,int i) { if(Number_entrys>MAX_NAMES){ printf("Please choose a smaller entry\n"); }else{ for (i=0; i<Number_entrys;i++){ scanf("%s",names[i]); } } } int search(char names[MAX_NAMES][MAX_NAMELENGTH],int Number_entrys) { int x; char new_name[MAX_NAMELENGTH]; printf("Now enter a name in which you would like to search the list for\n"); scanf("%s",new_name); for(x = 0; x < Number_entrys; x++) { if ( strcmp( new_name, names[x] ) == 0 ) { return x; } } return -1; } Like I mentioned before I have tried a lot of different ways to try and fix this issue, but I cant seem to get them to work. Printing X like what I have above is just the last thing I tried, and therefor know that it doesn't work. Any suggestions on the simplest way to do this?

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  • C -- Basic Struct questions

    - by Ryan Yu
    So I'm trying to learn C right now, and I have some basic struct questions I'd like to clear up: Basically, everything centers around this snippet of code: #include <stdio.h> #include <stdlib.h> #define MAX_NAME_LEN 127 typedef struct { char name[MAX_NAME_LEN + 1]; unsigned long sid; } Student; /* return the name of student s */ const char* getName (const Student* s) { // the parameter 's' is a pointer to a Student struct return s->name; // returns the 'name' member of a Student struct } /* set the name of student s If name is too long, cut off characters after the maximum number of characters allowed. */ void setName(Student* s, const char* name) { // 's' is a pointer to a Student struct | 'name' is a pointer to the first element of a char array (repres. a string) s->name = name; } /* return the SID of student s */ unsigned long getStudentID(const Student* s) { // 's' is a pointer to a Student struct return s->sid; } /* set the SID of student s */ void setStudentID(Student* s, unsigned long sid) { // 's' is a pointer to a Student struct | 'sid' is a 'long' representing the desired SID s->sid = sid; } I've commented up the code in an attempt to solidify my understanding of pointers; I hope they're all accurate. So anyway, I have a feeling that setName and setStudentID aren't correct, but I'm not exactly sure why. Can someone explain? Thanks!

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  • What is the ISO C++ way to directly define a conversion function to reference to array?

    - by ben
    According to the standard, a conversion function has a function-id operator conversion-type-id, which would look like, say, operator char(&)[4] I believe. But I cannot figure out where to put the function parameter list. gcc does not accept either of operator char(&())[4] or operator char(&)[4]() or anything I can think of. Now, gcc seems to accept (&operator char ())[4] but clang does not, and I am inclined to not either, since it does not seem to fit the grammar as I understand it. I do not want to use a typedef because I want to avoid polluting the namespace with it.

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  • Playing with Strings

    - by HARSHITH
    Given a string and a non-empty word string, return a string made of each char just before and just after every appearance of the word in the string. Ignore cases where there is no char before or after the word, and a char may be included twice if it is between two words. wordEnds("abcXY123XYijk", "XY") ? "c13i" wordEnds("XY123XY", "XY") ? "13" wordEnds("XY1XY", "XY") ? "11"

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  • "Forced constness" in std::map<std::vector<int>,double> > ?

    - by Peter Jansson
    Consider this program: #include <map> #include <vector> typedef std::vector<int> IntVector; typedef std::map<IntVector,double> Map; void foo(Map& m,const IntVector& v) { Map::iterator i = m.find(v); i->first.push_back(10); }; int main() { Map m; IntVector v(10,10); foo(m,v); return 0; } Using g++ 4.4.0, I get his compilation error: test.cpp: In function 'void foo(Map&, const IntVector&)': test.cpp:8: error: passing 'const std::vector<int, std::allocator<int> >' as 'this' argument of 'void std::vector<_Tp, _Alloc>::push_back(const _Tp&) [with _Tp = int, _Alloc = std::allocator<int>]' discards qualifiers I would expect this error if I was using Map::const_iterator inside foo but not using a non-const iterator. What am I missing, why do I get this error?

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  • how to structure code that uses std::rel_ops

    - by R Samuel Klatchko
    I was working on some code and wanted to make use of std::rel_ops. From what I can tell, you need to do using std::rel_ops to your source code to make use of them. But I'm not sure where the best place to put that is. Let's say I have a header file with a class that only defines the minimal operator== and operator<: // foo.h class foo { public: bool operator==(const foo &other) const; bool operator<(const foo &other) const; }; I'm not sure where to put using std::rel_ops. If I leave it out of the foo.h, then every user of foo.h needs to know the implementation detail that foo is not defining all the operators itself. But putting using std::rel_ops inside foo.h breaks the rule of thumb about not having a using in a header file. How do other people resolve this issue?

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  • Transmogrify into date from multiple columns

    - by Dave Jarvis
    What is a better way to program the following SQL: str_to_date( concat(convert(D.DAY, CHAR(2)), '-', convert(M.MONTH, CHAR(2)), '-', convert(M.YEAR, CHAR(4))), '%e-%m-%Y' ) as AMOUNT_DATE I want to convert the columns D.DAY, M.MONTH, and M.YEAR to a date field using MySQL. The above works, but seems much more complicated than it needs to be. (If there's an ANSI SQL way to do it, that would be even better.) Thank you!

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  • Unicode version of base64 encoding/ decoding

    - by Yan Cheng CHEOK
    I am using base64 encoding/decoding from http://www.adp-gmbh.ch/cpp/common/base64.html It works pretty well with the following code. const std::string s = "I Am A Big Fat Cat" ; std::string encoded = base64_encode(reinterpret_cast<const unsigned char*>(s.c_str()), s.length()); std::string decoded = base64_decode(encoded); std::cout << _T("encoded: ") << encoded << std::endl; std::cout << _T("decoded: ") << decoded << std::endl; However, when comes to unicode namespace std { #ifdef _UNICODE typedef wstring tstring; #else typedef string tstring; #endif } const std::tstring s = _T("I Am A Big Fat Cat"); How can I still make use of the above function? Merely changing std::string base64_encode(unsigned TCHAR const* , unsigned int len); std::tstring base64_decode(std::string const& s); will not work correctly. (I expect base64_encode to return ASCII. Hence, std::string should be used instead of std::tstring)

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  • Error building QtDeclarative with Qt 4.6.2 on Mac OS X

    - by Viet
    I tried hard to build QtDeclarative with Qt 4.6.2 on Mac OS X (Leopard) and did lots of Googling without finding any cure. Could anyone please help to solve this problem? Thanks. Here goes the error: Undefined symbols: "QObjectPrivate::isSignalConnected(int) const", referenced from: QmlGraphicsKeysAttachedPrivate::isConnected(char const*)in qmlgraphicsitem.o QmlGraphicsMouseRegionPrivate::isConnected(char const*)in qmlgraphicsmouseregion.o ld: symbol(s) not found collect2: ld returned 1 exit status make: *** [.obj/QtDeclarative.framework/QtDeclarative] Error 1

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  • how to allocate memory for struct itself, and its members

    - by Jack
    I have this struct: struct foo { char *a; char *b; char *c; char *d; }; it's possible allocate space for struct itself and its members instead of e.g, struct foo f; f.a = malloc(); f.b = malloc(); f.c = malloc(); f.d = malloc(); strcpy(f.a, "a"); strcpy(f.b, "b"); //.. something like this(of couse that it doesn't works): struct foo f = malloc(sizeof(struct f)); strpcy(f.a, "a"); //etc

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  • Compile time type determination in C++

    - by dicroce
    A coworker recently showed me some code that he found online. It appears to allow compile time determination of whether a type has an "is a" relationship with another type. I think this is totally awesome, but I have to admit that I'm clueless as to how this actually works. Can anyone explain this to me? template<typename BaseT, typename DerivedT> inline bool isRelated(const DerivedT&) { DerivedT derived(); char test(const BaseT&); // sizeof(test()) == sizeof(char) char (&test(...))[2]; // sizeof(test()) == sizeof(char[2]) struct conversion { enum { exists = (sizeof(test(derived())) == sizeof(char)) }; }; return conversion::exists; } Once this function is defined, you can use it like this: #include <iostream> class base {}; class derived : public base {}; class unrelated {}; int main() { base b; derived d; unrelated u; if( isRelated<base>( b ) ) std::cout << "b is related to base" << std::endl; if( isRelated<base>( d ) ) std::cout << "d is related to base" << std::endl; if( !isRelated<base>( u ) ) std::cout << "u is not related to base" << std::endl; }

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  • Should this work?

    - by Noah Roberts
    I am trying to specialize a metafunction upon a type that has a function pointer as one of its parameters. The code compiles just fine but it will simply not match the type. #include <iostream> #include <boost/mpl/bool.hpp> #include <boost/mpl/identity.hpp> template < typename CONT, typename NAME, typename TYPE, TYPE (CONT::*getter)() const, void (CONT::*setter)(TYPE const&) > struct metafield_fun {}; struct test_field {}; struct test { int testing() const { return 5; } void testing(int const&) {} }; template < typename T > struct field_writable : boost::mpl::identity<T> {}; template < typename CONT, typename NAME, typename TYPE, TYPE (CONT::*getter)() const > struct field_writable< metafield_fun<CONT,NAME,TYPE,getter,0> > : boost::mpl::false_ {}; typedef metafield_fun<test, test_field, int, &test::testing, 0> unwritable; int main() { std::cout << typeid(field_writable<unwritable>::type).name() << std::endl; std::cin.get(); } Output is always the type passed in, never bool_.

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  • The different of SHA512 between openssl and php

    - by solomon_wzs
    Here is C code: #include <openssl/sha.h> #include <stdio.h> char *hash_sha512(char *data){ SHA512_CTX ctx; char *md=malloc(sizeof(char)*(SHA512_DIGEST_LENGTH+1)); SHA512_Init(&ctx); SHA512_Update(&ctx, data, strlen(data)); SHA512_Final(md, &ctx); md[SHA512_DIGEST_LENGTH]='\0'; return md; } int main(int argc, char *argv[]){ str=hash_sha512("GFLOuJnR19881218"); printf("%s\n", str); free(str); return 1; } The output: ?<?4????IIA[r?? ?#? 6p?8jD????J?b9?????^X? Here is PHP code: $hash=hash('sha512', 'GFLOuJnR19881218', TRUE); The output: ?<??4??j??II?-A[r???? ??#??D6p?8jD???????J?b9?????^X? The results of C code and PHP code are different, what is wrong with my code?

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  • C++ get method - returning by value or by reference

    - by HardCoder1986
    Hello! I've go a very simple question, but unfortunately I can't figure the answer myself. Suppose I've got some data structure that holds settings and acts like a settings map. I have a GetValue(const std::string& name) method, that returns the corresponding value. Now I'm trying to figure out - what kind of return-value approach would be better. The obvious one means making my method act like std::string GetValue(const std::string& name) and return a copy of the object and rely on RVO in performance meanings. The other one would mean making two methods std::string& GetValue(...) const std::string& GetValue(...) const which generally means duplicating code or using some evil constant casts to use one of these routines twice. #Q What would be your choice in this kind of situation and why?

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  • Is allocating a dynamic array without specifying size well formed code?

    - by Als
    The following simple program snippet gives compilation errorswith gcc-4.3.4. Program: int main() { char *ptr = new char[10]; char *ptr1 = new char[]; return 0; } Compilation errors: prog.cpp: In function ‘int main()’: prog.cpp:4: error: expected primary-expression before ‘]’ token prog.cpp:3: warning: unused variable ‘ptr’ prog.cpp:4: warning: unused variable ‘ptr1’ But the same compiles cleanly with MSVC without any diagnostic message. So my question is: Does the Standard allow an new [] to be called without specifying the size? Or this a bug in MSVC? Can someone provide a reference from the standard which will conclusively say that the above code example is ill-formed or well-formed? I have had a look at: 5.3.4 New [expr.new] & 18.4.1.2 Array forms [lib.new.delete.array] but couldnt find any conclusive evidence about the behavior.

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  • Letter Count on a string

    - by user74283
    Python newb here. I m trying to count the number of letter "a"s in a given string. Code is below. It keeps returning 1 instead 3 in string "banana". Any input appreciated. def count_letters(word, char): count = 0 while count <= len(word): for char in word: if char == word[count]: count += 1 return count print count_letters('banana','a')

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  • Rotate a linked list

    - by user408041
    I want to rotate a linked list that contains a number. 123 should be rotated to 231. The function created 23 but the last character stays empty, why? typedef struct node node; struct node{ char digit; node* p; }; void rotate(node** head){ node* walk= (*head); node* prev= (*head); char temp= walk->digit; while(walk->p!=NULL){ walk->digit=walk->p->digit; walk= walk->p; } walk->digit=temp; } How I create the list: node* convert_to_list(int num){ node * curr, * head; int i=0,length=0; char *arr=NULL; head = NULL; length =(int) log10(((double) num))+1; arr =(char*) malloc((length)*sizeof(char)); //allocate memory sprintf (arr, "%d" ,num); //(num, buf, 10); for(i=length;i>=0;i--) { curr = (node *)malloc(sizeof(node)); (curr)->digit = arr[i]; (curr)->p = head; head = curr; } curr = head; return curr; }

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  • C++ Translation Phase Confusion

    - by blakecl
    Can someone explain why the following doesn't work? int main() // Tried on several recent C++ '03 compilers. { #define FOO L const wchar_t* const foo = FOO"bar"; // Will error out with something like: "identifier 'L' is undefined." #undef FOO } I thought that preprocessing was done in an earlier translation phase than string literal operations and general token translation. Wouldn't the compiler be more or less seeing this: int main() { const wchar_t* const foo = L"bar"; } It would be great if someone could cite an explanation from the standard.

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  • How to properly assign a value to the member of a struct that has a class data type?

    - by sasayins
    Hi, Please kindly see below for the codes. Its compiling successfully but the expected result is not working. Im very confused because my initialization of the array is valid, //cbar.h class CBar { public: class CFoo { public: CFoo( int v ) : m_val = v {} int GetVal() { return m_val; } private: int m_val; }; public: static const CFoo foo1; static const CFoo foo2; public: CBar( CFoo foo ) m_barval( foo.GetVal() ){} int GetFooVal() { return m_barval; } private: int m_barval; }; //cbar.cpp const CBar::CFoo foo1 = CBar::CFoo(2); const CBar::CFoo foo2 = CBar::CFoo(3); //main.cpp struct St { CBar::CFoo foo; }; St st[] = { CBar::foo1, CBar::foo2 }; for( int i=0; i<sizeof(st)/sizeof(St); i++ ) { CBar cbar( st[i].foo ); std::cout << cbar.GetFooVal() << std::endl; } But then when I change the St::foo to a pointer. And like assign the address of CBar::foo1 or CBar::foo2, its working, like this, //main.cpp struct St { const CBar::CFoo *foo; }; St st[] = { &CBar::foo1, &CBar::foo2 }; for( int i=0; i<sizeof(st)/sizeof(St); i++ ) { CBar cbar( *st[i].foo ); std::cout << cbar.GetFooVal() << std::endl; } The real problem is. The app should output 2 3 Please advice. Many thanks.

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  • C++ conversion operator between types in other libraries

    - by Dave
    For convenience, I'd like to be able to cast between two types defined in other libraries. (Specifically, QString from the Qt library and UnicodeString from the ICU library.) Right now, I have created utility functions in a project namespace: namespace MyProject { const icu_44::UnicodeString ToUnicodeString(const QString& value); const QString ToQString(const icu_44::UnicodeString& value); } That's all well and good, but I'm wondering if there's a more elegant way. Ideally, I'd like to be able to convert between them using a cast operator. I do, however, want to retain the explicit nature of the conversion. An implicit conversion should not be possible. Is there a more elegant way to achieve this without modifying the source code of the libraries? Some operator overload syntax, perhaps?

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