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  • Different types for declaring pointer variables

    - by viswanathan
    Consider the below 2 declarations. appears next to the datatype and not next to variable char* ptr1, * ptr2, * ptr3; //all 3 are pointers appears next to the variable and not next to datatype char *ptr1,*ptr2,*ptr3; //again al 3 are pointers Is there any difference in intepretation between the 2 declarations. I know there is no difference in the variables. What is the rationale behind introducing void pointers?

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  • pointer to a structure in a nested structure

    - by dpka6
    I have a 6 levels of nested structures. I am having problem with last three levels. The program compiles fine but when I run it crashes with Segmentation fault. There is some problem in assignment is what I feel. Kindly point out the error. typedef struct { char addr[6]; int32_t rs; uint16_t ch; uint8_t ap; } C; typedef struct { C *ap_info; } B; typedef struct { union { B wi; } u; } A; function1(char addr , int32_t rs, uint16_t ch, uint8_t ap){ A la; la.u.wi.ap_info->addr[6] = addr; la.u.wi.ap_info->rs = rs; la.u.wi.ap_info->ch = ch; la.u.wi.ap_info->ap = ap; }

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  • C++ arrays as parameters, subscript vs. pointer

    - by awshepard
    Alright, I'm guessing this is an easy question, so I'll take the knocks, but I'm not finding what I need on google or SO. I'd like to create an array in one place, and populate it inside a different function. I define a function: void someFunction(double results[]) { for (int i = 0; i<100; ++i) { for (int n = 0; n<16; ++n) //note this iteration limit { results[n] += i * n; } } } That's an approximation to what my code is doing, but regardless, shouldn't be running into any overflow or out of bounds issues or anything. I generate an array: double result[16]; for(int i = 0; i<16; i++) { result[i] = -1; } then I want to pass it to someFunction someFunction(result); When I set breakpoints and step through the code, upon entering someFunction, results is set to the same address as result, and the value there is -1.000000 as expected. However, when I start iterating through the loop, results[n] doesn't seem to resolve to *(results+n) or *(results+n*sizeof(double)), it just seems to resolve to *(results). What I end up with is that instead of populating my result array, I just get one value. What am I doing wrong?

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  • Auto pointer for unsigned char array?

    - by Gianluca
    I'd need a class like std::auto_ptr for an array of unsigned char*, allocated with new[]. But auto_ptr only calls delete and not delete[], so i can't use it. I also need to have a function which creates and returns the array. I came out with my own implementation within a class ArrayDeleter, which i use like in this example: #include <Utils/ArrayDeleter.hxx> typedef Utils::ArrayDeleter<unsigned char> Bytes; void f() { // Create array with new unsigned char* xBytes = new unsigned char[10]; // pass array to constructor of ArrayDeleter and // wrap it into auto_ptr return std::auto_ptr<Bytes>(new Bytes(xBytes)); } ... // usage of return value { auto_ptr<Bytes> xBytes(f()); }// unsigned char* is destroyed with delete[] in destructor of ArrayDeleter Is there a more elegant way to solve this? (Even using another "popular" library)

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  • How to change the meaning of pointer access operator

    - by kumar_m_kiran
    Hi All, This may be very obvious question, pardon me if so. I have below code snippet out of my project, #include <stdio.h> class X { public: int i; X() : i(0) {}; }; int main(int argc,char *arv[]) { X *ptr = new X[10]; unsigned index = 5; cout<<ptr[index].i<<endl; return 0; } Question Can I change the meaning of the ptr[index] ? Because I need to return the value of ptr[a[index]] where a is an array for subindexing. I do not want to modify existing source code. Any new function added which can change the behavior is needed. Since the access to index operator is in too many places (536 to be precise) in my code, and has complex formulas inside the index subscript operator, I am not inclined to change the code in many locations. PS : 1. I tried operator overload and came to conclusion that it is not possible. 2. Also p[i] will be transformed into *(p+i). I cannot redefine the basic operator '+'. So just want to reconfirm my understanding and if there are any possible short-cuts to achieve. Else I need fix it by royal method of changing every line of code :) .

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  • std::string constructor corrupts pointer

    - by computergeek6
    I have an Entity class, which contains 3 pointers: m_rigidBody, m_entity, and m_parent. Somewhere in Entity::setModel(std::string model), it's crashing. Apparently, this is caused by bad data in m_entity. The weird thing is that I nulled it in the constructor and haven't touched it since then. I debugged it and put a watchpoint on it, and it comes up that the m_entity member is being changed in the constructor for std::string that's being called while converting a const char* into an std::string for the setModel call. I'm running on a Mac, if that helps (I think I remember some problem with std::string on the Mac). Any ideas about what's going on?

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  • Null Pointer Exception in my BroadcastReceiver class

    - by user1760007
    I want to search a db and toast a specific column on the startup of the phone. The app keeps crashing and getting an exception even though I feel as the code is correct. @Override public void onReceive(Context ctx, Intent intent) { Log.d("omg", "1"); DBAdapter do = new DBAdapter(ctx); Log.d("omg", "2"); Cursor cursor = do.fetchAllItems(); Log.d("omg", "3"); if (cursor.moveToFirst()) { Log.d("omg", "4"); do { Log.d("omg", "5"); String title = cursor.getString(cursor.getColumnIndex("item")); Log.d("omg", "6"); // i = cursor.getInt(cursor.getColumnIndex("id")); Toast.makeText(ctx, title, Toast.LENGTH_LONG).show(); } while (cursor.moveToNext()); } cursor.close(); } The frustrating part is that I don't see any of my "omg" logs show up in logcat. I only see when my application crashes. I get three lines of errors in logcat. 10-19 12:31:11.656: E/AndroidRuntime(1471): java.lang.RuntimeException: Unable to start receiver com.test.toaster.MyReciever: java.lang.NullPointerException 10-19 12:31:11.656: E/AndroidRuntime(1471): at com.test.toaster.DBAdapter.fetchAllItems(DBAdapter.java:96) 10-19 12:31:11.656: E/AndroidRuntime(1471): at com.test.toaster.MyReciever.onReceive(MyReciever.java:26) For anyone interested, here is my DBAdapter fetchAllItems code: public Cursor fetchAllItems() { return mDb.query(DATABASE_TABLE, new String[] { KEY_ITEM, KEY_PRIORITY, KEY_ROWID }, null, null, null, null, null); }

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  • alertDialog.getButton() method gives null pointer exception android

    - by Are
    Hi, Iam planing to give create 3 buttons with layout_weight=1, not interested in custom dialog.So I have written below code.It is not working.Always yes button gives me null. Whats wrong in this code? AlertDialog dialog= new AlertDialog.Builder(this).create(); dialog.setIcon(R.drawable.alert_icon); dialog.setTitle("title"); dialog.setMessage("Message"); dialog.setButton(AlertDialog.BUTTON_POSITIVE,"Yes", new DialogInterface.OnClickListener() { @Override public void onClick(DialogInterface arg0, int arg1) { } }); Button yesButton = dialog.getButton(AlertDialog.BUTTON_POSITIVE); Log.w("Button",""+yesButton);//here getting null LinearLayout.LayoutParams layoutParams = new LinearLayout.LayoutParams(LayoutParams.FILL_PARENT, LayoutParams.WRAP_CONTENT, 1f); yesButton.setLayoutParams(layoutParams); dialog.show(); Regards, Android developer.

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  • C++ function-pointer and inheritance

    - by pingvinus
    In parent class I have function, that operates under an array of functions, declared in child-class, number of functions for every child-class may vary. But since every function uses some object-variables, I can't declare them as static. I've try to do something like this: class A { public: typedef int (A::*func)(); func * fs; void f() { /*call functions from this->fs*/ } }; class B : public A { public: int smth; B(int smth) { this->smth = smth; this->fs = new func[1]; fs[0] = &B::f; } int f() { return smth + 1; } }; But, obviously it doesn't work. Any suggestions?

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  • Objective-c pointer assignment and reassignment dilema

    - by moshe
    Hi, If I do this: 1 NSMutableArray *near = [[NSMutableArray alloc] init]; 2 NSMutableArray *all = [[NSMutableArray alloc] init]; 3 NSMutableArray *current = near; 4 current = all; What happens to near? At line 3, am I setting current to point to the same address as near so that I now have two variables pointing to the same place in memory, or am I setting current to point to the location of near in memory such that I now have this structure: current - near - NSMutableArray The obvious difference would be the value of near at line 4. If the former is happening, near is untouched and still points to its initial place in memory. If the latter is happening,

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  • EXC_BAD_ACCESS when simply casting a pointer in Obj-C

    - by AlexChilcott
    Hi all, Frequent visitor but first post here on StackOverflow, I'm hoping that you guys might be able to help me out with this. I'm fairly new to Obj-C and XCode, and I'm faced with this really... weird... problem. Googling hasn't turned up anything whatsoever. Basically, I get an EXC_BAD_ACCESS signal on a line that doesn't do any dereferencing or anything like that that I can see. Wondering if you guys have any idea where to look for this. I've found a work around, but no idea why this works... The line the broken version barfs out on is the line: LevelEntity *le = entity; where I get my bad access signal. Here goes: THIS VERSION WORKS NSArray *contacts = [self.body getContacts]; for (PhysicsContact *contact in contacts) { PhysicsBody *otherBody; if (contact.bodyA == self.body) { otherBody = contact.bodyB; } if (contact.bodyB == self.body) { otherBody = contact.bodyA; } id entity = [otherBody userData]; if (entity != nil) { LevelEntity *le = entity; CGPoint point = [contact contactPointOnBody:otherBody]; } } THIS VERSION DOESNT WORK NSArray *contacts = [self.body getContacts]; for (NSUInteger i = 0; i < [contacts count]; i++) { PhysicsContact *contact = [contacts objectAtIndex:i]; PhysicsBody *otherBody; if (contact.bodyA == self.body) { otherBody = contact.bodyB; } if (contact.bodyB == self.body) { otherBody = contact.bodyA; } id entity = [otherBody userData]; if (entity != nil) { LevelEntity *le = entity; CGPoint point = [contact contactPointOnBody:otherBody]; } } Here, the only difference between the two examples is the way I enumerate through my array. In the first version (which works) I use for (... in ...), where as in the second I use for (...; ...; ...). As far as I can see, these should be the same. This is seriously weirding me out. Anyone have any similar experience or idea whats going on here? Would be really great :) Cheers, Alex

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  • How to find an element in an array in C

    - by gkaykck
    I am trying to find the location of an element in the array. I have tried to use this code i generated for(i=0;i<10;i++) { if (strcmp(temp[0],varptr[i])==0) j=i; } varptr is a pointer which points to array var[11][10] and it is by the definition *varptr[11][10]. I have assigned strings to var[i] and i want to get the "i" number of my element NOT THE ADRESS. Thanks for any comment. EDit: temp is also a pointer which points to the string that i want to check. Also i am using the 2D array for keeping variable names and their address. So yes i want to keep it inside a 2D array. The question is this code is not working at all, it does not assigns i to j, so i wonder where is the problem with this idea? writing a "break" does not change if the code works or not, it just optimizes the code a little. Full Code: #include <stdio.h> #include <string.h> #include <ctype.h> double atof(char*); int main(void) { char in[100], *temp[10],var[11][10],*varptr[11][10]; int i,j, n = 0,fullval=0; double val[11]; strcpy(var[11], "ans"); for(i=0;i<11;i++) { for(j=0;j<10;j++) varptr[i][j]=&var[i][j]; } START: printf("Enter the expression: "); fflush(stdout); for(i=0;i<10;i++) temp[i]=NULL; if (fgets(in, sizeof in, stdin) != NULL) { temp[0] = strtok(in, " "); if (temp[0] != NULL) { for (n = 1; n < 10 && (temp[n] = strtok(NULL," ")) != NULL; n++) ; } if (*temp[0]=="quit") { goto FINISH;} if (isdigit(*temp[0])) { if (*temp[1]=='+') val[0] = atof(temp[0])+atof(temp[2]); else if (*temp[1]=='-') val[0] = atof(temp[0])-atof(temp[2]); else if (*temp[1]=='*') val[0] = atof(temp[0])*atof(temp[2]); else if (*temp[1]=='/') val[0] = atof(temp[0])/atof(temp[2]); printf("%s = %f\n",var[11],val[0]); goto START; } else if (temp[1]==NULL) //asking the value of a variable { for(i=0;i<10;i++) { if (strcmp(temp[0],varptr[i])==0) j=i; } printf("%s = %d\n",var[j],val[j]); goto START; } if (*temp[1]==61) { strcpy(var[fullval], temp[0]); if ((temp[3])!=NULL) { } val[fullval]=atof(temp[2]); printf("%s = %f\n",var[fullval],val[fullval]); fullval++; goto START; } if (*temp[1]!=61) { } } getch(); FINISH: return 0; }

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  • Cryptic C++ "thing" (function pointer)

    - by m00st
    What is this syntax for in C++? Can someone point me to the technical term so I can see if I find anything in my text? At first I thought it was a prototype but then the = and (*fn) threw me off... Here is my example: void (*fn) (int&,int&) = x;

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  • Initializing a char array through passed pointer segfaults

    - by Bitgarden
    Ie., why does the following work: char* char_array(size_t size){ return new char[size]; } int main(){ const char* foo = "foo"; size_t len = strlen(foo); char* bar=char_array(len); memset(bar, 0, len+1); } But the following segfaults: void char_array(char* out, size_t size){ out= new char[size]; } int main(){ const char* foo = "foo"; size_t len = strlen(foo); char* bar; char_array(bar, len); memset(bar, 0, len+1); }

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  • C++ print value of a pointer

    - by user69514
    I have an array of double pointers, but every time I try do print one of the values the address gets printed. How do I print the actual value? cout << arr[i] ? cout << &arr[i] ? they both print the address Does anyone know?

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  • "assignment makes integer from pointer without a cast " warning in c

    - by mekasperasky
    #include<stdio.h> /* this is a lexer which recognizes constants , variables ,symbols, identifiers , functions , comments and also header files . It stores the lexemes in 3 different files . One file contains all the headers and the comments . Another file will contain all the variables , another will contain all the symbols. */ int main() { int i=0,j; char a,b[20],c[30]; FILE *fp1,*fp2; c[0]='"if"; c[1]="then"; c[2]="else"; c[3]="switch"; c[4]="printf"; c[5]="scanf"; c[6]="NULL"; c[7]="int"; c[8]="char"; c[9]="float"; c[10]="long"; c[11]="double"; c[12]="char"; c[13]="const"; c[14]="continue"; c[15]="break"; c[16]="for"; c[17]="size of"; c[18]="register"; c[19]="short"; c[20]="auto"; c[21]="while"; c[22]="do"; c[23]="case"; fp1=fopen("source.txt","r"); //the source file is opened in read only mode which will passed through the lexer fp2=fopen("lext.txt","w"); //now lets remove all the white spaces and store the rest of the words in a file if(fp1==NULL) { perror("failed to open source.txt"); //return EXIT_FAILURE; } i=0; while(!feof(fp1)) { a=fgetc(fp1); if(a!=' ') { b[i]=a; } else { for (j=0;j<23;j++) { if(c[j]==b) { fprintf(fp2, "%.20s\n", c[j]); continue ; } b[i]='\0'; fprintf(fp2, "%.20s\n", b); i=0; continue; } //else if //{ i=i+1; /*Switch(a) { case EOF :return eof; case '+':sym=sym+1; case '-':sym=sym+1; case '*':sym=sym+1; case '/':sym=sym+1; case '%':sym=sym+1; case ' */ } fclose(fp1); fclose(fp2); return 0; } This is my c code for lexical analysis .. its giving warnings and also not writing anything into the lext file ..

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  • (gcc) Multi-Dim Array or Double Pointer for Warning-free Compile

    - by paul simmons
    Hi, I have a function, which is called sometimes with regular, sometimes dynamic arrays. If I define the function as function_name(int[10][10] a) and send int** as a parameter, I get a warning. Opposite, if I declare function_name(int** a) and send int[][] as a parameter (after casting) I cannot access to array elements inside function. What is the correctest way?

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  • Writing to pointer out of bounds after malloc() not causing error

    - by marr
    Hi, when I try the code below it works fine. Am I missing something? main() { int *p; p=malloc(sizeof(int)); printf("size of p=%d\n",sizeof(p)); p[500]=999999; printf("p[0]=%d",p[500]); return 0; } I tried it with malloc(0*sizeof(int)) or anything but it works just fine. The program only crashes when I don't use malloc at all. So even if I allocate 0 memory for the array p, it still stores values properly. So why am I even bothering with malloc then?

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  • c++ protected pointer member to the same class and access privileges

    - by aajmakin
    Hi, Example code is included at the bottom of the message. I'm puzzled about the protected access specifier in a class. I have define a class node which has a protected string member name string name; and a vector of node pointers vector args; Before I thought that a member function of node could not do args[0]-name but a program that does just this does compile and run. However, now I would like to inherit this class and access the name field in one of the args array pointers from this derived class args[0]-name but this does not compile. When I compile the example code below with the commented sections uncommented, the compiler reports: Compiler output: g++ test.cc -o test test.cc: In member function 'void foo::newnode::print_args2()': test.cc:22: error: 'std::string foo::node::name' is protected test.cc:61: error: within this context Compilation exited abnormally with code 1 at Thu Jun 17 12:40:12 Questions: Why can I access the name field of the node pointers in args in class node, because this is what I would excpect from a similarly defined private field in Java. How can I access those fields from the derived class. Example code: #include <iostream> #include <vector> using namespace std; namespace foo { class node; typedef std::vector<node*> nodes; class node { public: node (string _name); void print_args (); void add_node (node* a); protected: nodes args; string name; }; } foo::node::node (string _name) : args(0) { name = _name; } void foo::node::add_node (node* a) { args.push_back(a); } void foo::node::print_args () { for (int i = 0; i < args.size(); i++) { cout << "node " << i << ": " << args[i]->name << endl; } } // namespace foo // { // class newnode : public node // { // public: // newnode (string _name) : node(_name) {} // void print_args2 (); // protected: // }; // } // void foo::newnode::print_args2 () // { // for (int i = 0; i < args.size(); i++) // { // cout << "node " << i << ": " << args[i]->name << endl; // } // } int main (int argc, char** argv) { foo::node a ("a"); foo::node b ("b"); foo::node c ("c"); a.add_node (&b); a.add_node (&c); a.print_args (); // foo::newnode newa ("newa"); // foo::newnode newb ("newb"); // foo::newnode newc ("newc"); // newa.add_node (&newb); // newa.add_node (&newc); // newa.print_args2 (); return 0; }

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  • Typcast a null pointer to char*

    - by user326253
    Suppose I have a char* elem that is supposed to hold a char*, s.t. elem[0] = char*, elem[1...m]= more chars. Is there a way I can put a null ptr within char* elem? When I try to set elem = NULL, it gives me a type error because NULL is an int. Any help would be greatly appreciated!

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  • c# Wrapper to native c++ code, wrapping a parameter which is a pointer to an array

    - by mb300dturbo
    Hi, I have the following simple DLL in c++ un-managed code; extern "C" __declspec(dllexport) void ArrayMultiplier(float (*pointerArray)[3], int scalar, int length); void ArrayMultiplier(float (*pointerArray)[3], int scalar, int length) { for (int i = 0 ; i < length ; length++) { for (int j = 0; j < 3; j++) { pointerArray[i][j] = pointerArray[i][j] * scalar; } } } I have tried writing the following wrapper function for the above in c#: [DllImport("sample.dll")] public static extern void ArrayMultiplier(ref float elements, int scalar, int length); where elements is a 2 dimentional 3x3 array: public float[][] elements = { new float[] {2,5,3}, new float [] {4,8,6}, new float [] {5,28,3} }; The code given above compiles, but the program crashes when the wrapper function is called: Wrapper.ArrayMultiplier(ref elements, scalar, length); Please help me here, and tell me whats wrong with the code above, or how a wrapper can be written for a simple c++ function: void SimpleFunction(float (*pointerToArray)[3]); Thank you all in advance

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  • Read from file into pointer to struct

    - by cla barzu
    I need help with pointers in C. I have to read from a file, and fill an array with pointers to struct rcftp_msg . Since now I did the next things: struct rcftp_msg { uint8_t version; uint8_t flags; uint16_t len; uint8_t buffer[512]; }; struct rcftp_msg *windows [10]; pfile = fopen(file,"r"); // Open the file I have to read from the file into the buffer, but I don't know how to do it. I tried the next: for (i = 0; i <10; i++){ leng=fread (**windows[i]->buffer**,sizeof(uint8_t),512,pfile); } I think windows[i]-buffer is bad, cuz that don't work. Sorry for my bad English :(

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