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  • why am i getting a null pointer when converting string to int array?

    - by Sackling
    My main method: public static void main(String[] args) { Scanner input = new Scanner(System.in); String string1; string1 = input.next(); LargeInteger firstInt = new LargeInteger(string1); System.out.printf("First integer: %s \n", firstInt.display()); } LargeInteger class: public class LargeInteger { private int[] intArray; //convert the strings to array public LargeInteger(String s) { for (int i = 0; i < s.length(); i++) { intArray[i] = Character.digit(s.charAt(i), 10); // in base 10 } } //display the strings public String display() { String result = ""; for (int i = 0; i < intArray.length; i++) { result += intArray[i]; } return result.toString(); } }

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  • Is it safe to take the address of std::wstring's internal pointer?

    - by LCC
    I have an interface which is used like the following: if (SUCCEEDED(pInterface->GetSize(&size)) { wchar_t tmp = new wchar_t[size]; if (SUCCEEDED(pInterface->GetValue(tmp, size))) { std::wstring str = tmp; // do some work which doesn't throw } delete[] tmp; } Is it safe and portable to do this instead? if (SUCCEEDED(pInterface->GetSize(&size)) { std::wstring str; str.resize(size); if (SUCCEEDED(pInterface->GetValue(&str[0], size))) { // do some work } } Now, obviously this works (doesn't crash/corrupt memory) or I wouldn't have asked, but I'm mostly wanting to know if there's a compelling reason not to do this.

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  • Problem with C function of type char pointer, can someone explain?

    - by JJ
    Find the errors from following C function : char* f(int i) { int i; char buffer[20]; switch ( i ) { 1: strcpy( buffer, "string1"); 2: strcpy( buffer, "string2"); 3: strcpy( buffer, "string3"); default: strcpy(buffer, "defaultstring"); } return buffer; } this is c funtion not C++, I think it has to do with type conversion my compiler give warning that declaration of int i shadows a parameter.

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  • How can I configure the touchpad and keyboard settings on a Dell Inspiron 5110?

    - by Robik
    I am using ubuntu 11.10. I want the following 3 things: I have dell inspiron 5110 laptop. There is button at the top right corner of laptop which can be used for turning the screen off. It works in windows but it does not work in ubuntu 11.10. Even in the manual of the laptop, it the button is supported only in windows. Is there a way to activate it in ubuntu 11.10? Some of the keys like: "break" etc. are missing. Can I use other keys (or combinations of other keys) to function as those missing keys? In the program, "mouse and touchpad", there is no tab for touchpad. I want to enable vertical and horizontal scrolling. How do I do that? The command: xinput list shows Virtual core pointer id=2 [master pointer (3)] ? ? Virtual core XTEST pointer id=4 [slave pointer (2)] ? ? PS/2 Generic Mouse id=13 [slave pointer (2)] ? Virtual core keyboard id=3 [master keyboard (2)] ? Virtual core XTEST keyboard id=5 [slave keyboard (3)] ? Power Button id=6 [slave keyboard (3)] ? Video Bus id=7 [slave keyboard (3)] ? Video Bus id=8 [slave keyboard (3)] ? Power Button id=9 [slave keyboard (3)] ? Sleep Button id=10 [slave keyboard (3)] ? Laptop_Integrated_Webcam_HD id=11 [slave keyboard (3)] ? AT Translated Set 2 keyboard id=12 [slave keyboard (3)] ? Dell WMI hotkeys Please help!!

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

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

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  • How can I declare a pointer with filled information in C++?

    - by chacham15
    typedef struct Pair_s { char *first; char *second; } Pair; Pair pairs[] = { {"foo", "bar"}, //this is fine {"bar", "baz"} }; typedef struct PairOfPairs_s { Pair *first; Pair *second; } PairOfPairs; PairOfPairs pops[] = { {{"foo", "bar"}, {"bar", "baz"}}, //How can i create an equivalent of this NEATLY {&pairs[0], &pairs[1]} //this is not considered neat (imagine trying to read a list of 30 of these) }; How can I achieve the above style declaration semantics?

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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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  • Assigning a pointer variable to a const int in C++?

    - by John
    I'm wondering if anyone can explain the following to me: If I write int i = 0; float* pf = i; I get a compile error (gcc 4.2.1): error: invalid conversion from ‘int’ to ‘float*’ Makes sense - they are obviously two completely different types. But if instead I write const int i = 0; float* pf = i; It compiles without error. Why should the 'const' make a difference on the right hand side of the assignment? Isn't part of the idea of the 'const' keyword to be able to enforce type constraints for constant values? Any explanation I have been able to come up with feels kind of bogus. And none of my explanations also explain the fact that const int i = 1; float* pf = i; fails to compile. Can anyone offer an explanation?

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  • Writting a getter for a pointer to a function .

    - by nomemory
    I have the following problem: "list.c" struct nmlist_element_s { void *data; struct nmlist_element_s *next; }; struct nmlist_s { nmlist_element *head; nmlist_element *tail; unsigned int size; void (*destructor)(void *data); int (*match)(const void *e1, const void *e2); }; /*** Other code ***/ What will be the signature for a function that returns 'destructor' ?

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  • Should I pointer-cast from a private derived class to its base class?

    - by skydoor
    I found this from C++FAQ Generally, No. From a member function or friend of a privately derived class, the relationship to the base class is known, and the upward conversion from PrivatelyDer* to Base* (or PrivatelyDer& to Base&) is safe; no cast is needed or recommended. However users of PrivatelyDer should avoid this unsafe conversion, since it is based on a private decision of PrivatelyDer, and is subject to change without notice. How to understand the above words? I don't think the explanation is correct or accurate. I have a code like this class A{ }; class B: private A{ }; int main(){ B *b = new B(); A *a = new A(); a = b; //wrong a = (A*)b; //right }

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  • Null pointer to struct which has zero size (empty)... It is a good practice?

    - by ProgramWriter
    Hi2All.. I have some null struct, for example: struct null_type { NullType& someNonVirtualMethod() { return *this; } }; And in some function i need to pass reference to this type. Reason: template <typename T1 = null_type, typename T2 = null_type, ... > class LooksLikeATupleButItsNotATuple { public: LooksLikeATupleButItsNotATuple(T1& ref1 = defParamHere, T2& ref2 = andHere..) : _ref1(ref1), _ref2(ref2), ... { } void someCompositeFunctionHere() { _ref1.someNonVirtualMethod(); _ref2.someNonVirtualMethod(); ... } private: T1& _ref1; T2& _ref2; ...; }; It is a good practice to use null reference as a default parameter?: *static_cast<NullType*>(0) It works on MSVC, but i have some doubts...

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  • Incorrect data when passing pointer a list of pointers to a function. (C++)

    - by Phil Elm
    I'm writing code for combining data received over multiple sources. When the objects received (I'll call them MyPacket for now), they are stored in a standard list. However, whenever I reference the payload size of a partial MyPacket, the value shows up as 1 instead of the intended size. Here's the function code: MyPacket* CombinePackets(std::list<MyPacket*>* packets, uint8* current_packet){ uint32 total_payload_size = 0; if(packets->size() <= 0) return NULL; //For now. std::list<MyPacket*>::iterator it = packets->begin(); //Some minor code here, not relevant to the problem. for(uint8 index = 0; index < packets->size(); index++){ //(*it)->GetPayloadSize() returns 1 when it should show 1024. I've tried directly accessing the variable and more, but I just can't get it to work. total_payload_size += (*it)->GetPayloadSize(); cout << "Adding to total payload size value: " << (*it)->GetPayloadSize() << endl; std::advance(it,1); } MyPacket* packet = new MyPacket(); //Byte is just a typedef'd unsigned char. packet->payload = (byte) calloc(total_payload_size, sizeof(byte)); packet->payload_size = total_payload_size; it = packets->begin(); //Go back to the beginning again. uint32 big_payload_index = 0; for(uint8 index = 0; index < packets->size(); index++){ if(current_packet != NULL) *current_packet = index; for(uint32 payload_index = 0; payload_index < (*it)->GetPayloadSize(); payload_index++){ packet->payload[big_payload_index] = (*it)->payload[payload_index]; big_payload_index++; } std::advance(it,1); } return packet; } //Calling code std::list<MyPacket*> received = std::list<MyPacket*>(); //The code that fills it is here. std::list<MyPacket*>::iterator it = received.begin(); cout << (*it)->GetPayloadSize() << endl; // Outputs 1024 correctly! MyPacket* final = CombinePackets(&received,NULL); cout << final->GetPayloadSize() << endl; //Outputs 181, which happens to be the number of elements in the received list. So, as you can see above, when I reference (*it)-GetPayloadSize(), it returns 1 instead of the intended 1024. Can anyone see the problem and if so, do you have an idea on how to fix this? I've spent 4 hours searching and trying new solutions, but they all keep returning 1... EDIT:

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  • MIPS return address in main

    - by Alexander
    I am confused why in the code below I need to decrement the stack pointer and store the return address again. If I don't do that... then PCSpim keeps on looping.. Why is that? ######################################################################################################################## ### main ######################################################################################################################## .text .globl main main: addi $sp, $sp, -4 # Make space on stack sw $ra, 0($sp) # Save return address # Start test 1 ############################################################ la $a0, asize1 # 1st parameter: address of asize1[0] la $a1, frame1 # 2nd parameter: address of frame1[0] la $a2, window1 # 3rd parameter: address of window1[0] jal vbsme # call function # Printing $v0 add $a0, $v0, $zero # Load $v0 for printing li $v0, 1 # Load the system call numbers syscall # Print newline. la $a0, newline # Load value for printing li $v0, 4 # Load the system call numbers syscall # Printing $v1 add $a0, $v1, $zero # Load $v1 for printing li $v0, 1 # Load the system call numbers syscall # Print newline. la $a0, newline # Load value for printing li $v0, 4 # Load the system call numbers syscall # Print newline. la $a0, newline # Load value for printing li $v0, 4 # Load the system call numbers syscall ############################################################ # End of test 1 lw $ra, 0($sp) # Restore return address addi $sp, $sp, 4 # Restore stack pointer jr $ra # Return ######################################################################################################################## ### vbsme ######################################################################################################################## #.text .globl vbsme vbsme: addi $sp, $sp, -4 # create space on the stack pointer sw $ra, 0($sp) # save return address exit: add $v1, $t5, $zero # (v1) x coordinate of the block in the frame with the minimum SAD add $v0, $t4, $zero # (v0) y coordinate of the block in the frame with the minimum SAD lw $ra, 0($sp) # restore return address addi $sp, $sp, 4 # restore stack pointer jr $ra # return If I delete: addi $sp, $sp, -4 # create space on the stack pointer sw $ra, 0($sp) # save return address and lw $ra, 0($sp) # restore return address addi $sp, $sp, 4 # restore stack pointer on vbsme: PCSpim keeps on running... Why??? I shouldn't have to increment/decrement the stack pointer on vbsme and then do the jr again right? The jal in main is supposed to handle that

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  • Is it valid to use unsafe struct * as an opaque type instead of IntPtr in .NET Platform Invoke?

    - by David Jeske
    .NET Platform Invoke advocates declaring pointer types as IntPtr. For example, the following [DllImport("user32.dll")] static extern IntPtr SendMessage(IntPtr hWnd, UInt32 Msg, Int32 wParam, Int32 lParam); However, I find when interfacing with interesting native interfaces, that have many pointer types, flattening everything into IntPtr makes the code very hard to read and removes the typical typechecking that a compiler can do. I've been using a pattern where I declare an unsafe struct to be an opaque pointer type. I can store this pointer type in a managed object, and the compiler can typecheck it form me. For example: class Foo { unsafe struct FOO {}; // opaque type unsafe FOO *my_foo; class if { [DllImport("mydll")] extern static unsafe FOO* get_foo(); [DllImport("mydll")] extern static unsafe void do_something_foo(FOO *foo); } public unsafe Foo() { this.my_foo = if.get_foo(); } public unsafe do_something_foo() { if.do_something_foo(this.my_foo); } While this example may not seem different than using IntPtr, when there are several pointer types moving between managed and native code, using these opaque pointer types for typechecking is a godsend. I have not run into any trouble using this technique in practice. However, I also have not seen an examples of anyone using this technique, and I wonder why. Is there any reason that the above code is invalid in the eyes of the .NET runtime? My main question is about how the .NET GC system treats "unsafe FOO *my_foo". Is this pointer something the GC system is going to try to trace, or is it simply going to ignore it? My hope is that because the underlying type is a struct, and it's declared unsafe, that the GC would ignore it. However, I don't know for sure. Thoughts?

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  • Python — Time complexity of built-in functions versus manually-built functions in finite fields

    - by stackuser
    Generally, I'm wondering about the advantages versus disadvantages of using the built-in arithmetic functions versus rolling your own in Python. Specifically, I'm taking in GF(2) finite field polynomials in string format, converting to base 2 values, performing arithmetic, then output back into polynomials as string format. So a small example of this is in multiplication: Rolling my own: def multiply(a,b): bitsa = reversed("{0:b}".format(a)) g = [(b<<i)*int(bit) for i,bit in enumerate(bitsa)] return reduce(lambda x,y: x+y,g) Versus the built-in: def multiply(a,b): # a,b are GF(2) polynomials in binary form .... return a*b #returns product of 2 polynomials in gf2 Currently, operations like multiplicative inverse (with for example 20 bit exponents) take a long time to run in my program as it's using all of Python's built-in mathematical operations like // floor division and % modulus, etc. as opposed to making my own division, remainder, etc. I'm wondering how much of a gain in efficiency and performance I can get by building these manually (as shown above). I realize the gains are dependent on how well the manual versions are built, that's not the question. I'd like to find out 'basically' how much advantage there is over the built-in's. So for instance, if multiplication (as in the example above) is well-suited for base 10 (decimal) arithmetic but has to jump through more hoops to change bases to binary and then even more hoops in operating (so it's lower efficiency), that's what I'm wondering. Like, I'm wondering if it's possible to bring the time down significantly by building them myself in ways that maybe some professionals here have already come across.

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  • How to call different methods from single webservices class

    - by pointer
    I have a following RESTful webservice, I have two methods for http get. One function signs in and other function signs out a user from an application. Following is the code: import javax.ws.rs.core.Context; import javax.ws.rs.core.UriInfo; import javax.ws.rs.PathParam; import javax.ws.rs.Consumes; import javax.ws.rs.PUT; import javax.ws.rs.Path; import javax.ws.rs.GET; import javax.ws.rs.POST; import javax.ws.rs.Produces; import javax.ws.rs.QueryParam; /** * REST Web Service * * @author Pointer */ @Path("generic") public class GenericResource { @Context private UriInfo context; /** * Creates a new instance of GenericResource */ public GenericResource() { } /** * Retrieves representation of an instance of * com.ef.apps.xmpp.ws.GenericResource * * @return an instance of java.lang.String */ @GET @Produces("text/html") public String SignIn(@QueryParam("username") String username, @QueryParam("password") String password, @QueryParam("extension") String extension) { //TODO return proper representation object return "Credentials " + username + " : " + password + " : " + extension; } @GET @Produces("text/html") public String SignOut(@QueryParam("username") String username, @QueryParam("password") String password, @QueryParam("extension") String extension) { //TODO return proper representation object return "Credentials " + username + " : " + password + " : " + extension; } } Now, where would I specify that which function I want to call for http get?

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