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  • User reduced LVM logical volume without resizing filesystem

    - by Matthew
    I received an email yesterday that one of our users was trying to make room for a heartbeat/clustering package which requires its own partition to act as a voting disk. To do this, he attempted to reduce the size of the root partition's logical volume, and then create a new logical volume for this purpose. However, he forgot to resize the filesystem first (or include the -r switch in the command). He also forgot to unmount the root partition by running this process from a rescue cd. The system is now refusing to boot into the OS with the following error: Either the superblock or the partition table is likely to be corrupt! Unexpected Inconsistency; run fsck manually. The system them drops the user into single user mode. Is it possible to rescue the filesystem, or is it hosed? Its running ext3.

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  • "reduce" or "apply" using logical functions in Clojure

    - by Alex B
    I cannot use logical functions on a range of booleans in Clojure (1.2). Neither of the following works due to logical functions being macros: (reduce and [... sequence of bools ...]) (apply or [... sequence of bools ...]) The error saying that I "can't take value of a macro: #'clojure.core/and". How to apply these logical functions (macros) without writing boilerplate code?

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  • How to recover logical volume deleted with lvremove

    - by John P
    I am on CentOS 5.5 and am running Xen. I have a large volume group that I create logical volumes on using lvcreate. Today I had a customer cancel her account, then change her mind about an hour later. Unfortunately I had already removed the LVM her Xen image resided on. (just using a standard lvremove ). There has been no other LVM activity on this disk since then (nothing else added or deleted). Is it possible to "undo" a lvremove, or recover logical volume? If so, how would I go about it?

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  • Is there a Generic USB TouchScreen Driver 12.04?

    - by lbjoum
    Is there a Generic USB TouchScreen Driver 12.04? Device 03eb:201c I've been looking for 4 days solid (not very skilled) and can't find a solution. I have a generic tablet: C97- Atom N2600 9.7" 2GB 32GB Bluetooth WiFi WebCam Ext.3G Windows 7 Tablet PC Using 12.04 and cannot find a driver. I installed android and the touchscreen works but still lots of other bugs. Oh well, stuck with Windows 7 and not happy about it. Will keep trying, but too much time wasted already. If you have a solution I would love to try it. ubuntu@ubuntu:~$ lsusb Bus 001 Device 001: ID 1d6b:0002 Linux Foundation 2.0 root hub Bus 002 Device 001: ID 1d6b:0001 Linux Foundation 1.1 root hub Bus 003 Device 001: ID 1d6b:0001 Linux Foundation 1.1 root hub Bus 004 Device 001: ID 1d6b:0001 Linux Foundation 1.1 root hub Bus 005 Device 001: ID 1d6b:0001 Linux Foundation 1.1 root hub Bus 001 Device 002: ID 0cf2:6238 ENE Technology, Inc. Bus 001 Device 003: ID 1a40:0101 Terminus Technology Inc. 4-Port HUB Bus 001 Device 005: ID 05e1:0100 Syntek Semiconductor Co., Ltd 802.11g + Bluetooth Wireless Adapter Bus 001 Device 006: ID 090c:3731 Silicon Motion, Inc. - Taiwan (formerly Feiya Technology Corp.) Bus 003 Device 002: ID 03eb:201c Atmel Corp. at90usbkey sample firmware (HID mouse) (from Windows: HID\VID_03EB&PID_201C\6&5F38127&0&0000 USB\VID_03EB&PID_201C\5&193ADADC&1&2 ) Bus 001 Device 007: ID 0518:0001 EzKEY Corp. USB to PS2 Adaptor v1.09 Bus 001 Device 008: ID 192f:0916 Avago Technologies, Pte. ubuntu@ubuntu:~$ sudo lsusb -v Bus 003 Device 002: ID 03eb:201c Atmel Corp. at90usbkey sample firmware (HID mouse) Device Descriptor: bLength 18 bDescriptorType 1 bcdUSB 2.00 bDeviceClass 0 (Defined at Interface level) bDeviceSubClass 0 bDeviceProtocol 0 bMaxPacketSize0 32 idVendor 0x03eb Atmel Corp. idProduct 0x201c at90usbkey sample firmware (HID mouse) bcdDevice 45.a2 iManufacturer 1 CDT iProduct 2 9.75 iSerial 0 bNumConfigurations 1 Configuration Descriptor: bLength 9 bDescriptorType 2 wTotalLength 34 bNumInterfaces 1 bConfigurationValue 1 iConfiguration 0 bmAttributes 0x00 (Missing must-be-set bit!) (Bus Powered) MaxPower 100mA Interface Descriptor: bLength 9 bDescriptorType 4 bInterfaceNumber 0 bAlternateSetting 0 bNumEndpoints 1 bInterfaceClass 3 Human Interface Device bInterfaceSubClass 0 No Subclass bInterfaceProtocol 0 None iInterface 0 HID Device Descriptor: bLength 9 bDescriptorType 33 bcdHID 1.11 bCountryCode 0 Not supported bNumDescriptors 1 bDescriptorType 34 Report wDescriptorLength 177 Report Descriptors: ** UNAVAILABLE ** Endpoint Descriptor: bLength 7 bDescriptorType 5 bEndpointAddress 0x81 EP 1 IN bmAttributes 3 Transfer Type Interrupt Synch Type None Usage Type Data wMaxPacketSize 0x0020 1x 32 bytes bInterval 5 Device Status: 0x00fb Self Powered Remote Wakeup Enabled Debug Mode ubuntu@ubuntu:~$ sudo lshw ubuntu description: Notebook product: To be filled by O.E.M. (To be filled by O.E.M.) vendor: To be filled by O.E.M. version: To be filled by O.E.M. serial: To be filled by O.E.M. width: 32 bits capabilities: smbios-2.7 dmi-2.7 smp-1.4 smp configuration: boot=normal chassis=notebook cpus=2 family=To be filled by O.E.M. sku=To be filled by O.E.M. uuid=00020003-0004-0005-0006-000700080009 *-core description: Motherboard product: Tiger Hill vendor: INTEL Corporation physical id: 0 version: To be filled by O.E.M. serial: To be filled by O.E.M. slot: To be filled by O.E.M. *-firmware description: BIOS vendor: American Megatrends Inc. physical id: 0 version: 4.6.5 date: 08/24/2012 size: 64KiB capacity: 960KiB capabilities: pci upgrade shadowing cdboot bootselect socketedrom edd int13floppy1200 int13floppy720 int13floppy2880 int5printscreen int9keyboard int14serial int17printer acpi usb biosbootspecification *-cpu:0 description: CPU product: Intel(R) Atom(TM) CPU N2600 @ 1.60GHz vendor: Intel Corp. physical id: 4 bus info: cpu@0 version: 6.6.1 serial: 0003-0661-0000-0000-0000-0000 slot: CPU 1 size: 1600MHz capacity: 1600MHz width: 64 bits clock: 400MHz capabilities: x86-64 boot fpu fpu_exception wp vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov pat pse36 clflush dts acpi mmx fxsr sse sse2 ss ht tm pbe nx constant_tsc arch_perfmon pebs bts nonstop_tsc aperfmperf pni dtes64 monitor ds_cpl est tm2 ssse3 cx16 xtpr pdcm movbe lahf_lm arat configuration: cores=2 enabledcores=1 id=2 threads=2 *-cache:0 description: L1 cache physical id: 5 slot: L1-Cache size: 24KiB capacity: 24KiB capabilities: internal write-back unified *-cache:1 description: L2 cache physical id: 6 slot: L2-Cache size: 512KiB capacity: 512KiB capabilities: internal varies unified *-logicalcpu:0 description: Logical CPU physical id: 2.1 width: 64 bits capabilities: logical *-logicalcpu:1 description: Logical CPU physical id: 2.2 width: 64 bits capabilities: logical *-logicalcpu:2 description: Logical CPU physical id: 2.3 width: 64 bits capabilities: logical *-logicalcpu:3 description: Logical CPU physical id: 2.4 width: 64 bits capabilities: logical *-memory description: System Memory physical id: 28 slot: System board or motherboard size: 2GiB *-bank:0 description: SODIMM [empty] product: [Empty] vendor: [Empty] physical id: 0 serial: [Empty] slot: DIMM0 *-bank:1 description: SODIMM DDR3 Synchronous 800 MHz (1.2 ns) vendor: 69 physical id: 1 serial: 00000210 slot: DIMM1 size: 2GiB width: 64 bits clock: 800MHz (1.2ns) *-cpu:1 physical id: 1 bus info: cpu@1 version: 6.6.1 serial: 0003-0661-0000-0000-0000-0000 size: 1600MHz capabilities: ht configuration: id=2 *-logicalcpu:0 description: Logical CPU physical id: 2.1 capabilities: logical *-logicalcpu:1 description: Logical CPU physical id: 2.2 capabilities: logical *-logicalcpu:2 description: Logical CPU physical id: 2.3 capabilities: logical *-logicalcpu:3 description: Logical CPU physical id: 2.4 capabilities: logical *-pci description: Host bridge product: Atom Processor D2xxx/N2xxx DRAM Controller vendor: Intel Corporation physical id: 100 bus info: pci@0000:00:00.0 version: 03 width: 32 bits clock: 33MHz *-display UNCLAIMED description: VGA compatible controller product: Atom Processor D2xxx/N2xxx Integrated Graphics Controller vendor: Intel Corporation physical id: 2 bus info: pci@0000:00:02.0 version: 09 width: 32 bits clock: 33MHz capabilities: pm msi vga_controller bus_master cap_list configuration: latency=0 resources: memory:dfe00000-dfefffff ioport:f100(size=8) *-multimedia description: Audio device product: N10/ICH 7 Family High Definition Audio Controller vendor: Intel Corporation physical id: 1b bus info: pci@0000:00:1b.0 version: 02 width: 64 bits clock: 33MHz capabilities: pm msi pciexpress bus_master cap_list configuration: driver=snd_hda_intel latency=0 resources: irq:42 memory:dff00000-dff03fff *-pci:0 description: PCI bridge product: N10/ICH 7 Family PCI Express Port 1 vendor: Intel Corporation physical id: 1c bus info: pci@0000:00:1c.0 version: 02 width: 32 bits clock: 33MHz capabilities: pci pciexpress msi pm normal_decode bus_master cap_list configuration: driver=pcieport resources: irq:40 ioport:2000(size=4096) memory:80000000-801fffff ioport:80200000(size=2097152) *-usb:0 description: USB controller product: N10/ICH 7 Family USB UHCI Controller #1 vendor: Intel Corporation physical id: 1d bus info: pci@0000:00:1d.0 version: 02 width: 32 bits clock: 33MHz capabilities: uhci bus_master configuration: driver=uhci_hcd latency=0 resources: irq:23 ioport:f0a0(size=32) *-usb:1 description: USB controller product: N10/ICH 7 Family USB UHCI Controller #2 vendor: Intel Corporation physical id: 1d.1 bus info: pci@0000:00:1d.1 version: 02 width: 32 bits clock: 33MHz capabilities: uhci bus_master configuration: driver=uhci_hcd latency=0 resources: irq:19 ioport:f080(size=32) *-usb:2 description: USB controller product: N10/ICH 7 Family USB UHCI Controller #3 vendor: Intel Corporation physical id: 1d.2 bus info: pci@0000:00:1d.2 version: 02 width: 32 bits clock: 33MHz capabilities: uhci bus_master configuration: driver=uhci_hcd latency=0 resources: irq:18 ioport:f060(size=32) *-usb:3 description: USB controller product: N10/ICH 7 Family USB UHCI Controller #4 vendor: Intel Corporation physical id: 1d.3 bus info: pci@0000:00:1d.3 version: 02 width: 32 bits clock: 33MHz capabilities: uhci bus_master configuration: driver=uhci_hcd latency=0 resources: irq:16 ioport:f040(size=32) *-usb:4 description: USB controller product: N10/ICH 7 Family USB2 EHCI Controller vendor: Intel Corporation physical id: 1d.7 bus info: pci@0000:00:1d.7 version: 02 width: 32 bits clock: 33MHz capabilities: pm debug ehci bus_master cap_list configuration: driver=ehci_hcd latency=0 resources: irq:23 memory:dff05000-dff053ff *-pci:1 description: PCI bridge product: 82801 Mobile PCI Bridge vendor: Intel Corporation physical id: 1e bus info: pci@0000:00:1e.0 version: e2 width: 32 bits clock: 33MHz capabilities: pci subtractive_decode bus_master cap_list *-isa description: ISA bridge product: NM10 Family LPC Controller vendor: Intel Corporation physical id: 1f bus info: pci@0000:00:1f.0 version: 02 width: 32 bits clock: 33MHz capabilities: isa bus_master cap_list configuration: latency=0 *-storage description: SATA controller product: N10/ICH7 Family SATA Controller [AHCI mode] vendor: Intel Corporation physical id: 1f.2 bus info: pci@0000:00:1f.2 logical name: scsi0 version: 02 width: 32 bits clock: 66MHz capabilities: storage msi pm ahci_1.0 bus_master cap_list emulated configuration: driver=ahci latency=0 resources: irq:41 ioport:f0f0(size=8) ioport:f0e0(size=4) ioport:f0d0(size=8) ioport:f0c0(size=4) ioport:f020(size=16) memory:dff04000-dff043ff *-disk description: ATA Disk product: BIWIN SSD physical id: 0.0.0 bus info: scsi@0:0.0.0 logical name: /dev/sda version: 1206 serial: 123403501060 size: 29GiB (32GB) capabilities: partitioned partitioned:dos configuration: ansiversion=5 signature=8fbe402b *-volume:0 description: Windows NTFS volume physical id: 1 bus info: scsi@0:0.0.0,1 logical name: /dev/sda1 version: 3.1 serial: 249bde5d-8246-9a40-88c7-2d5e3bcaf692 size: 19GiB capacity: 19GiB capabilities: primary bootable ntfs initialized configuration: clustersize=4096 created=2011-04-04 02:27:51 filesystem=ntfs state=clean *-volume:1 description: Windows NTFS volume physical id: 2 bus info: scsi@0:0.0.0,2 logical name: /dev/sda2 version: 3.1 serial: de12d40f-d5ca-8642-b306-acd9349fda1a size: 10231MiB capacity: 10GiB capabilities: primary ntfs initialized configuration: clustersize=4096 created=2011-04-04 01:52:26 filesystem=ntfs state=clean *-serial UNCLAIMED description: SMBus product: N10/ICH 7 Family SMBus Controller vendor: Intel Corporation physical id: 1f.3 bus info: pci@0000:00:1f.3 version: 02 width: 32 bits clock: 33MHz configuration: latency=0 resources: ioport:f000(size=32) *-scsi:0 physical id: 2 bus info: usb@1:1 logical name: scsi4 capabilities: emulated scsi-host configuration: driver=usb-storage *-disk description: SCSI Disk physical id: 0.0.0 bus info: scsi@4:0.0.0 logical name: /dev/sdb size: 29GiB (31GB) capabilities: partitioned partitioned:dos configuration: signature=00017463 *-volume description: Windows FAT volume vendor: mkdosfs physical id: 1 bus info: scsi@4:0.0.0,1 logical name: /dev/sdb1 logical name: /cdrom version: FAT32 serial: 129b-4f87 size: 29GiB capacity: 29GiB capabilities: primary bootable fat initialized configuration: FATs=2 filesystem=fat mount.fstype=vfat mount.options=rw,relatime,fmask=0022,dmask=0022,codepage=cp437,iocharset=iso8859-1,shortname=mixed,errors=remount-ro state=mounted *-scsi:1 physical id: 3 bus info: usb@1:3.1 logical name: scsi6 capabilities: emulated scsi-host configuration: driver=usb-storage *-disk description: SCSI Disk physical id: 0.0.0 bus info: scsi@6:0.0.0 logical name: /dev/sdc size: 7400MiB (7759MB) capabilities: partitioned partitioned:dos configuration: signature=c3072e18 *-volume description: Windows FAT volume vendor: mkdosfs physical id: 1 bus info: scsi@6:0.0.0,1 logical name: /dev/sdc1 logical name: /media/JOUM8G version: FAT32 serial: e676-9311 size: 7394MiB capacity: 7394MiB capabilities: primary bootable fat initialized configuration: FATs=2 filesystem=fat label=Android mount.fstype=vfat mount.options=rw,nosuid,nodev,relatime,uid=999,gid=999,fmask=0022,dmask=0077,codepage=cp437,iocharset=iso8859-1,shortname=mixed,showexec,utf8,flush,errors=remount-ro state=mounted ubuntu@ubuntu:~$ ubuntu@ubuntu:~$ xinput list ? Virtual core pointer id=2 [master pointer (3)] ? ? Virtual core XTEST pointer id=4 [slave pointer (2)] ? ? Plus More Enterprise LTD. USB-compliant keyboard id=10 [slave pointer (2)] ? ? USB Optical Mouse id=11 [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)] ? Power Button id=7 [slave keyboard (3)] ? Sleep Button id=8 [slave keyboard (3)] ? Plus More Enterprise LTD. USB-compliant keyboard id=9 [slave keyboard (3)] ? USB 2.0 Webcam - Front id=12 [slave keyboard (3)] ? AT Translated Set 2 keyboard id=13 [slave keyboard (3)] ubuntu@ubuntu:~$

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  • What are the best practices for implementing the == operator for a class in C#?

    - by remio
    While implementing an == operator, I have the feeling that I am missing some essential points. Hence, I am searching some best practices around that. Here are some related questions I am thinking about: How to cleanly handle the reference comparison? Should it be implemented through a IEquatable<T>-like interface? Or overriding object.Equals? And what about the != operator? (this list might not be exhaustive).

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  • How Does iPhone Visual Voicemail Work From An Operator Perspective?

    - by Jasarien
    I'm hoping there are some Cell Phone Operator gurus here today. Would anyone be able to explain how Operators achieve the Visual Voicemail feature on the iPhone (and I assume other newer smart phones)? If a new cell phone operator that distributed SIM cards wanted to utilise the visual voicemail feature on unlocked iPhone's what services need to be in place to be able to support it? Is there an open spec or is it completely proprietary?

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  • "AND Operator" in PAM

    - by d_inevitable
    I need to prevent users from authenticating through Kerberos when the encrypted /home/users has not yet been mounted. (This is to avoid corrupting the ecryptfs mountpoint) Currently I have these lines in /etc/pam.d/common-auth: auth required pam_group.so use_first_pass auth [success=2 default=ignore] pam_krb5.so minimum_uid=1000 try_first_pass auth [success=1 default=ignore] pam_unix.so nullok_secure try_first_pass I am planning to use pam_exec.so to execute a script that will exit 1 if the ecyptfs mounts are not ready yet. Doing this: auth required pam_exec.so /etc/security/check_ecryptfs will lock me out for good if ecryptfs for some reason fails. In such case I would like to at least be able to login with a local (non-kerberos) user to fix the issue. Is there some sort of AND-Operator in which I can say that login through kerberos+ldap is only sufficient if both kerberos authentication and the ecryptfs mount has succeeded?

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  • Avoid Postfix Increment Operator

    - by muntoo
    I've read that I should avoid the postfix increment operator because of performance reasons (in certain cases). But doesn't this affect code readability? In my opinion: for(int i = 0; i < 42; i++); /* i will never equal 42! */ Looks better than: for(int i = 0; i < 42; ++i); /* i will never equal 42! */ But this is probably just out of habit. Admittedly, I haven't seen many use ++i. Is the performance that bad to sacrifice readability, in this case? Or am I just blind, and ++i is more readable than i++?

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  • Why does virtual assignment behave differently than other virtual functions of the same signature?

    - by David Rodríguez - dribeas
    While playing with implementing a virtual assignment operator I have ended with a funny behavior. It is not a compiler glitch, since g++ 4.1, 4.3 and VS 2005 share the same behavior. Basically, the virtual operator= behaves differently than any other virtual function with respect to the code that is actually being executed. struct Base { virtual Base& f( Base const & ) { std::cout << "Base::f(Base const &)" << std::endl; return *this; } virtual Base& operator=( Base const & ) { std::cout << "Base::operator=(Base const &)" << std::endl; return *this; } }; struct Derived : public Base { virtual Base& f( Base const & ) { std::cout << "Derived::f(Base const &)" << std::endl; return *this; } virtual Base& operator=( Base const & ) { std::cout << "Derived::operator=( Base const & )" << std::endl; return *this; } }; int main() { Derived a, b; a.f( b ); // [0] outputs: Derived::f(Base const &) (expected result) a = b; // [1] outputs: Base::operator=(Base const &) Base & ba = a; Base & bb = b; ba = bb; // [2] outputs: Derived::operator=(Base const &) Derived & da = a; Derived & db = b; da = db; // [3] outputs: Base::operator=(Base const &) ba = da; // [4] outputs: Derived::operator=(Base const &) da = ba; // [5] outputs: Derived::operator=(Base const &) } The effect is that the virtual operator= has a different behavior than any other virtual function with the same signature ([0] compared to [1]), by calling the Base version of the operator when called through real Derived objects ([1]) or Derived references ([3]) while it does perform as a regular virtual function when called through Base references ([2]), or when either the lvalue or rvalue are Base references and the other a Derived reference ([4],[5]). Is there any sensible explanation to this odd behavior?

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  • operator new for array of class without default constructor......

    - by skydoor
    For a class without default constructor, operator new and placement new can be used to declare an array of such class. When I read the code in More Effective C++, I found the code as below(I modified some part)..... My question is, why [] after the operator new is needed? I test it without it, it still works. Can any body explain that? class A { public: int i; A(int i):i(i) {} }; int main() { void *rawMemory = operator new[] (10 * sizeof(A)); // Why [] needed here? A *p = static_cast<A*>(rawMemory); for(int i = 0 ; i < 10 ; i++ ) { new(&p[i])A(i); } for(int i = 0 ; i < 10 ; i++ ) { cout<<p[i].i<<endl; } for(int i = 0 ; i < 10 ; i++ ) { p[i].~A(); } return 0; }

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  • Where to add an overloaded operator for the tr1::array?

    - by phlipsy
    Since I need to add an operator& for the std::tr1::array<bool, N> I wrote the following lines template<std::size_t N> std::tr1::array<bool, N> operator& (const std::tr1::array<bool, N>& a, const std::tr1::array<bool, N>& b) { std::tr1::array<bool, N> result; std::transform(a.begin(), a.end(), b.begin(), result.begin(), std::logical_and<bool>()); return result; } Now I don't know in which namespace I've to put this function. I considered the std namespace as a restricted area. Only total specialization and overloaded function templates are allowed to be added by the user. Putting it into the global namespace isn't "allowed" either in order to prevent pollution of the global namespace and clashes with other declarations. And finally putting this function into the namespace of the project doesn't work since the compiler won't find it there. What had I best do? I don't want to write a new array class putted into the project namespace. Because in this case the compiler would find the right namespace via argument dependent name lookup. Or is this the only possible way because writing a new operator for existing classes means extending their interfaces and this isn't allowed either for standard classes?

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  • Operator overloading in generic struct: can I create overloads for specific kinds(?) of generic?

    - by Carson Myers
    I'm defining physical units in C#, using generic structs, and it was going okay until I got the error: One of the parameters of a binary operator must be the containing type when trying to overload the mathematical operators so that they convert between different units. So, I have something like this: public interface ScalarUnit { } public class Duration : ScalarUnit { } public struct Scalar<T> where T : ScalarUnit { public readonly double Value; public Scalar(double Value) { this.Value = Value; } public static implicit operator double(Scalar<T> Value) { return Value.Value; } } public interface VectorUnit { } public class Displacement : VectorUnit { } public class Velocity : VectorUnit { } public struct Vector<T> where T : VectorUnit { #... public static Vector<Velocity> operator /(Vector<Displacement> v1, Scalar<Duration> v2) { return new Vector<Velocity>(v1.Magnitude / v2, v1.Direction); } } There aren't any errors for the + and - operators, where I'm just working on a Vector<T>, but when I substitute a unit for T, suddenly it doesn't like it. Is there a way to make this work? I figured it would work, since Displacement implements the VectorUnit interface, and I have where T : VectorUnit in the struct header. Am I at least on the right track here? I'm new to C# so I have difficulty understanding what's going on sometimes.

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  • Conversion constructor vs. conversion operator: precedence

    - by GRB
    Reading some questions here on SO about conversion operators and constructors got me thinking about the interaction between them, namely when there is an 'ambiguous' call. Consider the following code: class A; class B { public: B(){} B(const A&) //conversion constructor { cout << "called B's conversion constructor" << endl; } }; class A { public: operator B() //conversion operator { cout << "called A's conversion operator" << endl; return B(); } }; int main() { B b = A(); //what should be called here? apparently, A::operator B() return 0; } The above code displays "called A's conversion operator", meaning that the conversion operator is called as opposed to the constructor. If you remove/comment out the operator B() code from A, the compiler will happily switch over to using the constructor instead (with no other changes to the code). My questions are: Since the compiler doesn't consider B b = A(); to be an ambiguous call, there must be some type of precedence at work here. Where exactly is this precedence established? (a reference/quote from the C++ standard would be appreciated) From an object-oriented philosophical standpoint, is this the way the code should behave? Who knows more about how an A object should become a B object, A or B? According to C++, the answer is A -- is there anything in object-oriented practice that suggests this should be the case? To me personally, it would make sense either way, so I'm interested to know how the choice was made. Thanks in advance

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  • Dilemma with two types and operator +

    - by user35443
    I have small problem with operators. I have this code: public class A { public string Name { get; set; } public A() { } public A(string Name) { this.Name = Name; } public static implicit operator B(A a) { return new B(a.Name); } public static A operator+(A a, A b) { return new A(a.Name + " " + b.Name); } } public class B { public string Name { get; set; } public B() { } public B(string Name) { this.Name = Name; } public static implicit operator A(B b) { return new A(b.Name); } public static B operator +(B b, B a) { return new B(b.Name + " " + a.Name); } } Now I want to know, which's conversion operator will be called and which's addition operator will be called in this operation: new A("a") + new B("b"); Will it be operator of A, or of B? (Or both?) Thanks....

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  • How to modify a given class to use const operators

    - by zsero
    I am trying to solve my question regarding using push_back in more than one level. From the comments/answers it is clear that I have to: Create a copy operator which takes a const argument Modify all my operators to const But because this header file is given to me there is an operator what I cannot make into const. It is a simple: float & operator [] (int i) { return _item[i]; } In the given program, this operator is used to get and set data. My problem is that because I need to have this operator in the header file, I cannot turn all the other operators to const, what means I cannot insert a copy operator. How can I make all my operators into const, while preserving the functionality of the already written program? Here is the full declaration of the class: class Vector3f { float _item[3]; public: float & operator [] (int i) { return _item[i]; } Vector3f(float x, float y, float z) { _item[0] = x ; _item[1] = y ; _item[2] = z; }; Vector3f() {}; Vector3f & operator = ( const Vector3f& obj) { _item[0] = obj[0]; _item[1] = obj[1]; _item[2] = obj[2]; return *this; }; Vector3f & operator += ( const Vector3f & obj) { _item[0] += obj[0]; _item[1] += obj[1]; _item[2] += obj[2]; return *this; }; bool operator ==( const Vector3f & obj) { bool x = (_item[0] == obj[0]) && (_item[1] == obj[1]) && (_item[2] == obj[2]); return x; } // my copy operator Vector3f(const Vector3f& obj) { _item[0] += obj[0]; _item[1] += obj[1]; _item[2] += obj[2]; return this; } };

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  • convert a logical partition to a primary partition

    - by ant2009
    Hello, Fedora 14 xfce I have the following partition setup. I would like to know how can I convert the logical partition sda6 to a primary partition. Disk /dev/sda: 320.1 GB, 320072933376 bytes 255 heads, 63 sectors/track, 38913 cylinders, total 625142448 sectors Units = sectors of 1 * 512 = 512 bytes Sector size (logical/physical): 512 bytes / 512 bytes I/O size (minimum/optimal): 512 bytes / 512 bytes Disk identifier: 0x1707a8a5 Device Boot Start End Blocks Id System /dev/sda1 2048 1026047 512000 83 Linux /dev/sda2 1026048 205844479 102409216 83 Linux /dev/sda3 205844480 214228991 4192256 82 Linux swap / Solaris /dev/sda4 214228992 625141759 205456384 5 Extended /dev/sda5 214231040 573562879 179665920 83 Linux /dev/sda6 573564928 625141759 25788416 7 HPFS/NTFS Filesystem Size Used Avail Use% Mounted on /dev/sda2 97G 5.0G 91G 6% / tmpfs 494M 176K 494M 1% /dev/shm /dev/sda1 485M 68M 392M 15% /boot /dev/sda5 169G 26G 135G 16% /home # partition table of /dev/sda unit: sectors /dev/sda1 : start= 2048, size= 1024000, Id=83 /dev/sda2 : start= 1026048, size=204818432, Id=83 /dev/sda3 : start=205844480, size= 8384512, Id=82 /dev/sda4 : start=214228992, size=410912768, Id= 5 /dev/sda5 : start=214231040, size=359331840, Id=83 /dev/sda6 : start=573564928, size= 51576832, Id= 7 I would like to convert sda6 to a primary partition, the reason for this it to install windows 7 starter. Many thanks for any suggestions,

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  • Creating a Logical network diagram

    - by user273284
    Im a student and I have been assigned the task of creating a logical network diagram for the following scenario There are 2 buildings, the first is the head office and the second is the branch. The data centre is in the head office, it contains domain controller, mail server, file server and a web server. it provides wired and wireless access to the staff. the branch building is new and it does not have a network. The two buildings must be connected using a VPN connection. The branch building will not have any servers but just network devices that will provide the connectivity, the users in the branch building will be connected to the head office over the VPN. I had created a diagram based on this scenario, but my teacher rejected it saying that it does not follow Cisco hierarchical Model and the servers were not placed correctly in the diagram. I just wanted some help in this matter so that I Can create my network diagram correctly. If anyone could upload a picture of how the logical diagram should be for this scenario will be helpful, any other resources would also be great.

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  • DIVIDE vs division operator in #dax

    - by Marco Russo (SQLBI)
    Alberto Ferrari wrote an interesting article about DIVIDE performance in DAX. This new function has been introduced in SQL Server Analysis Services 2012 SP1, so it is available also in Excel 2013 (which still doesn’t have other features/fixes introduced by following Cumulative Updates…). The idea that instead of writing: IF ( Sales[Quantity] <> 0, Sales[Amount] / Sales[Quantity], BLANK () ) you can write: DIVIDE ( Sales[Amount], Sales[Quantity] ) There is a third optional argument in DIVIDE that defines the result in case the denominator (second argument) is zero, and by default its value is BLANK, so I omitted the third argument in my example. Using DIVIDE is very important, especially when you use a measure in MDX (for example in an Excel PivotTable) because it raise the chance that the non empty evaluation for the result is evaluated in bulk mode instead of cell-by-cell. However, from a DAX point of view, you might find it’s better to use the standard division operator removing the IF statement. I suggest you to read Alberto’s article, because you will find that an expression applying a filter using FILTER is faster than using CALCULATE, which is against any rule of thumb you might have read until now! Again, this is not always true, and depends on many conditions – trying to simplify, we might say that for a simple calculation, the query plan generated by FILTER could be more efficient – but, as usual, it depends, and 90% of the times using FILTER instead of CALCULATE produces slower performance. Do not take anything for granted, and always check the query plan when performance are your first issue!

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  • SQL SERVER – Fix: Error: 8117: Operand data type bit is invalid for sum operator

    - by pinaldave
    Here is the very interesting error I received from a reader. He has very interesting question. He attempted to use BIT filed in the SUM aggregation function and he got following error. He went ahead with various different datatype (i.e. INT, TINYINT etc) and he was able to do the SUM but with BIT he faced the problem. Error Received: Msg 8117, Level 16, State 1, Line 1 Operand data type bit is invalid for sum operator. Reproduction of the error: Set up the environment USE tempdb GO -- Preparing Sample Data CREATE TABLE TestTable (ID INT, Flag BIT) GO INSERT INTO TestTable (ID, Flag) SELECT 1, 0 UNION ALL SELECT 2, 1 UNION ALL SELECT 3, 0 UNION ALL SELECT 4, 1 GO SELECT * FROM TestTable GO Following script will work fine: -- This will work fine SELECT SUM(ID) FROM TestTable GO However following generate error: -- This will generate error SELECT SUM(Flag) FROM TestTable GO The workaround is to convert or cast the BIT to INT: -- Workaround of error SELECT SUM(CONVERT(INT, Flag)) FROM TestTable GO Clean up the setup -- Clean up DROP TABLE TestTable GO Workaround: As mentioned in above script the workaround is to covert the bit datatype to another friendly data types like INT, TINYINT etc. Reference: Pinal Dave (http://blog.sqlauthority.com) Filed under: PostADay, SQL, SQL Authority, SQL Query, SQL Server, SQL Tips and Tricks, T SQL, Technology

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  • Implicit conversion while using += operator?

    - by bdhar
    Conside the following code: int main() { signed char a = 10; a += a; // Line 5 a = a + a; return 0; } I am getting this warning at Line 5: d:\codes\operator cast\operator cast\test.cpp(5) : warning C4244: '+=' : conversion from 'int' to 'signed char', possible loss of data Does this mean that += operator makes an implicit cast of the right hand operator to int? P.S: I am using Visual studio 2005

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  • Is there an "opposite" to the null coalescing operator? (…in any language?)

    - by Jay
    null coalescing translates roughly to return x, unless it is null, in which case return y I often need return null if x is null, otherwise return x.y I can use return x == null ? null : x.y; Not bad, but that null in the middle always bothers me -- it seems superfluous. I'd prefer something like return x :: x.y;, where what follows the :: is evaluated only if what precedes it is not null. I see this as almost an opposite to null coalescence, kind of mixed in with a terse, inline null-check, but I'm [almost] certain that there is no such operator in C#. Are there other languages that have such an operator? If so, what is it called? (I know that I can write a method for it in C#; I use return NullOrValue.of(x, () => x.y);, but if you have anything better, I'd like to see that too.)

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