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• Reading function pointer syntax

  - by bobobobo

  Everytime I look at a C function pointer, my eyes glaze over. I can't read them. From here, here are 2 examples of function pointer TYPEDEFS: typedef int (*AddFunc)(int,int); typedef void (*FunctionFunc)(); Now I'm used to something like: typedef vector<int> VectorOfInts ; Which I read as typedef vector<int> /* as */ VectorOfInts ; But I can't read the above 2 typedefs. The bracketing and the asterisk placement, it's just not logical. Why is the * beside the word AddFunc..?

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• What happens when you deallocate a reference twice or more in c++?

  - by flopex

  int main(){ Employee *e = new Employee(); delete e; delete e; ... delete e; return 0; }

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• enable_shared_from_this and inheritance

  - by DeadMG

  I've got a type which inherits from enable_shared_from_this<type>, and another type that inherits from this type. Now I can't use the shared_from_this method because it returns the base type and in a specific derived class method I need the derived type. Is it valid to just construct a shared_ptr from this directly? Edit: In a related question, how can I move from an rvalue of type shared_ptr<base> to a type of shared_ptr<derived>? I used dynamic_cast to verify that it really was the correct type, but now I can't seem to accomplish the actual move.

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• What happens when you deallocate a pointer twice or more in C++?

  - by flopex

  int main(){ Employee *e = new Employee(); delete e; delete e; ... delete e; return 0; }

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• C++: Print only one char

  - by Martijn Courteaux

  Hi, When I read one char* from std::cin and I want to write it to std::cout, it prints until it finds a \0 in memory. So what did was: char c; cin >> c; char* pChar = &c; pChar++; *pChar = '\0'; println(&c); // My own method: void println(char * str) { cout << str << endl; } But I don't think this is a safe action. Is there a safer way to do this?

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• Better variant of getting the output dinamically-allocated array from the function?

  - by Raigomaru

  Here is to variants. First: int n = 42; int* some_function(int* input) { int* result = new int[n]; // some code return result; } void main() { int* input = new int[n]; int* output = some_function(input); delete[] input; delete[] output; } Here the function returns the memory, allocated inside the function. Second variant: int n = 42; void some_function(int* input, int* output) { // some code } void main() { int* input = new int[n]; int* output = new int[n]; some_function(input, output); delete[] input; delete[] output; } Here the memory is allocated outside the function. Now I use the first variant. But I now that many built-in c++ functions use the second variant. The first variant is more comfortable (in my opinion). But the second one also has some advantages (you allocate and delete memory in the same block). Maybe it's a silly question but what variant is better and why?

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• Add 64 bit offset to a pointer

  - by Novox

  In F#, there's the NativePtr module, but it seems to only support 32 bit offsets for its’ add/get/set functions, just like System.IntPtr does. Is there a way to add a 64 bit offset to a native pointer (nativeptr<'a) in F#? Of course I could convert all addresses to 64 bit integers, do normal integer operations and then convert the result again to nativeptr<'a, but this would cost additional add and imul instructions. I really want the AGUs to perform the address calculations. For instance, using unsafe in C# you could do something like void* ptr = Marshal.AllocHGlobal(...).ToPointer(); int64 offset = ...; T* newAddr = (T*)ptr + offset; // T has to be an unmanaged type Well actually you can't, because there is no "unmanaged" constraint for type parameters, but at least you can do general pointer arithmetic in a non-generic way. In F# we finally got the unmanaged constraint; but how do I do the pointer arithmetic?

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• Can I access type int (*)[] with [][]?

  - by Framester

  Hi coming from this question "What does (int (*)[])var1 stand for?" I tried to access the result of the cast like a multidimensional array. But I get following error: "assignment from incompatible pointer type" followed by a segmentation fault. I tried also some other variations, but none of them worked. How can I access the elements in var1 in the function example directly? Thank you! #include <stdlib.h> int i(int n,int m,int var1[n][m]) { var1[0][0]=5; return var1[0][0]; } int example() { int *var1 = malloc(100); // works int var2; var2 = i(10,10,(int (*)[])var1); printf("var2=%i",var2); //doesn't work I int *var3; var3=(int (*)[])var1; //"assignment from incompatible pointer type" printf("var3[0][0]=%i",var3[0][0]); //doesn't work II int *var4; var4=var1; printf("var4[0][0]=%i",var4[0][0]); //" error: subscripted value is neither array nor pointer" //doesn't work III int **var5; var5=var1; printf("var5[0][0]=%i",var5[0][0]); // assignment from incompatible pointer type return(1); } int main(){ int a; a=example(); return(1); }

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• C++: Validate a pointer?

  - by Rosarch

  If I have a pointer, like char* foo, is there any way to determine if foo points to a valid location in memory? (So, foo is not NULL, and delete has not yet been called on it.)

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• What is better: to delete pointer or set it with a new value?

  - by user63898

  Hi simple question in c++ , say i have a loop and i have function that returns pointer to item so i have to define inner loop pointer so my question is what to do with the pointer inside the loop , delete it ? or to set it with new value is good for example: for(int i =0;i<count();i++) { ptrTmp* ptr = getItemPtr(); // do somthing with the ptr ... // what to do here ? to delete the poinetr or not? delete ptr; // ?? }

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• How to convert a void pointer to array of classes

  - by user99545

  I am trying to convert a void pointer to an array of classes in a callback function that only supports a void pointer as a means of passing paramaters to the callback. class person { std::string name, age; }; void callback (void *val) { for (int i = 0; i < 9; i++) { std::cout << (person [])val[i].name; } } int main() { person p[10]; callback((void*)p); } My goal is to be able to pass an array of the class person to the callback which then prints out the data such as their name and age. However, the compile does not like what I am doing and complains that error: request for member 'name' in 'val', which is of non-class type 'void*' How can I go about doing this?

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• base pointer to derived class

  - by Jay

  Suppose there are Base class and Derived class. Base *A = new Base; Here A is a pointer point to Base class, and new constructs one that A points to. I also saw Base *B = new Derived; How to explain this? B is a pointer to Base Class, and a Derived class constructed and pointed by B? If there is a function derived from Base class, say, Virtual void f(), and it's been overridden in Derived class, then B->f() will invoke which version of the function? version in Base class, or version that overridden in Derived Class. What if there is a new function void g()in Derived, is B->g() going to invoke this function properly? One more is, is int *a = new double; or int *a = new int; legal?

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• Doubt regarding usage of array as a pointer in C

  - by Som

  For eg. I have an array of structs 'a' as below: struct mystruct{ int b int num; }; struct bigger_struct { struct my_struct a[10]; } struct bigger_struct *some_var; i know that the name of an array when used as a value implicitly refers to the address of the first element of the array.(Which is how the array subscript operator works at-least) Can i know do the other way around i.e if i do: some_var->a->b, it should be equivalent to some_var->a[0]->b, am i right? I have tested this and it seems to work , but is this semantically 100% correct?

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• What is purpose of a this pointer in C++ ?

  - by de costo

  What is purpose of this keyword. Doesn't the methods in a class have access to other peer members in the same class ? WHat is the need to call a this to call peer methods inside a class ??

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• make it simpler and efficient

  - by gcc

  temp1=*tutar[1]; //i hold input in char *tutar[] if(temp1!='x'||temp1!='n') arrays[1]=malloc(sizeof(int)*num_arrays); //if second input is int a=0; n=i; for(i=1;i<n;++i) { temp1=*tutar[i]; if(temp1=='d') { ++i; j=atoi(tutar[i]); free(arrays[j]); continue; } if(temp1=='x') break; if(temp1=='n')//if it is n { a=0; ++j; arrays[j]=malloc(sizeof(int)*num_arrays);//create and allocate continue; } ++a; if(a>num_arrays) //resize the array arrays[j]=realloc(arrays[j],sizeof(int)*(num_arrays+a)); *(arrays[j]+a-1)=atoi(tutar[i]); printf("%d",arrays[1][1]); } arrays is pointer when you see x exit you see n create (old one is new array[a] new one is array[i+1]) you see d delete arrays[i] according to int after d first number is size of max arrays and where is the error in code input is composed from int and n d x i make a program -taking input(first input must be int) -according to input(there is comman in input like n or d or j , i fill array with number and use memory efficiently -j is jumb to array[x] ( x is int coming after j in input)

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• NullPointerException

  - by Knowing me knowing you

  Why do I get exception called NullPointerException if in Java there is no such concept as a pointer? Thanks

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• Any pitfalls using char* instead of void* when writing cross platform code?

  - by UberMongoose

  Is there any pitfalls when using char*'s to write cross platform code that does memory access? I'm working on a play memory allocator to better understand how to debug memmory issues. I have come to believe char*'s are preferable because of the ability to do pointer arithmetic and derefernce them over void*'s, is that true? Do the following assumptions always hold true on different common platforms? sizeof(char) == 1 sizeof(char*) == sizeof(void*) sizeof(char*) == sizeof(size_t)

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• Virtual functions - base class pointer

  - by user980411

  I understood why a base class pointer is made to point to a derived class object. But, I fail to understand why we need to assign to it, a base class object, when it is a base class object by itself. Can anyone please explain that? #include <iostream> using namespace std; class base { public: virtual void vfunc() { cout << "This is base's vfunc().\n"; } }; class derived1 : public base { public: void vfunc() { cout << "This is derived1's vfunc().\n"; } }; int main() { base *p, b; derived1 d1; // point to base p = &b; p->vfunc(); // access base's vfunc() // point to derived1 p = &d1; p->vfunc(); // access derived1's vfunc() return 0; }

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• Cannot determine why pointer variable will not address elements in a string in this program?

  - by Smith Will Suffice

  I am attempting to utilize a pointer variable to access elements of a string and there are issues with my code generating a compilation error: #include <stdio.h> #define MAX 29 char arrayI[250]; char *ptr; int main(void) { ptr = arrayI; puts("Enter string to arrayI: up to 29 chars:\n"); fgets(arrayI, MAX, stdin); printf("\n Now printing array by pointer:\n"); printf("%s", *ptr); ptr = arrayI[1]; //(I set the pointer to the second array char element) printf("%c", *ptr); //Here is where I was wanting to use my pointer to //point to individual array elements. return 0; } My compiler crieth: [Warning] assignment makes pointer from integer without a cast [enabled by default] I do not see where my pointer was ever assigned to the integer data type? Could someone please explain why my attempt to implement a pointer variable is failing? Thanks all!

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• Using traversal by pointer to check whether a string is repeated

  - by Bob John

  bool repeat_char(char *s, int n); //R: s is a C-string of at least n non-NUL characters and n > 0 //E: returns true if the first n characters are fully repeated throughout the string s, false // otherwise. I'm having trouble implementing this function using traversal by pointer. I was thinking that I could extract the first n characters from s, then use that in a comparison with s, but I'm not sure how I could do that. If I'm traversing through s one character at a time, how can I check that it matches a block of text, such as the first n characters of s? Thanks!

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• in c++ what is bettr to delete poiner or set it with new value?

  - by user63898

  Hi simple question in c++ , say i have a loop and i have function that returns pointer to item so i have to define inner loop pointer so my question is what to do with the pointer inside the loop , delete it ? or to set it with new value is good for example: for(int i =0;i<count();i++) { ptrTmp* ptr = getItemPtr(); // do somthing with the ptr ... // what to do here ? to delete the poinetr or not? delete ptr; // ?? }

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• laptop crashed: why?

  - by sds

  my linux (ubuntu 12.04) laptop crashed, and I am trying to figure out why. # last sds pts/4 :0 Tue Sep 4 10:01 still logged in sds pts/3 :0 Tue Sep 4 10:00 still logged in reboot system boot 3.2.0-29-generic Tue Sep 4 09:43 - 11:23 (01:40) sds pts/8 :0 Mon Sep 3 14:23 - crash (19:19) this seems to indicate a crash at 09:42 (= 14:23+19:19). as per another question, I looked at /var/log: auth.log: Sep 4 09:17:02 t520sds CRON[32744]: pam_unix(cron:session): session closed for user root Sep 4 09:43:17 t520sds lightdm: pam_unix(lightdm:session): session opened for user lightdm by (uid=0) no messages file syslog: Sep 4 09:24:19 t520sds kernel: [219104.819975] CPU0: Package power limit normal Sep 4 09:43:16 t520sds kernel: imklog 5.8.6, log source = /proc/kmsg started. kern.log: Sep 4 09:24:19 t520sds kernel: [219104.819969] CPU1: Package power limit normal Sep 4 09:24:19 t520sds kernel: [219104.819971] CPU2: Package power limit normal Sep 4 09:24:19 t520sds kernel: [219104.819974] CPU3: Package power limit normal Sep 4 09:24:19 t520sds kernel: [219104.819975] CPU0: Package power limit normal Sep 4 09:43:16 t520sds kernel: imklog 5.8.6, log source = /proc/kmsg started. Sep 4 09:43:16 t520sds kernel: [ 0.000000] Initializing cgroup subsys cpuset Sep 4 09:43:16 t520sds kernel: [ 0.000000] Initializing cgroup subsys cpu I had a computation running until 9:24, but the system crashed 18 minutes later! kern.log has many pages of these: Sep 4 09:43:16 t520sds kernel: [ 0.000000] total RAM covered: 8086M Sep 4 09:43:16 t520sds kernel: [ 0.000000] gran_size: 64K chunk_size: 64K num_reg: 10 lose cover RAM: 38M Sep 4 09:43:16 t520sds kernel: [ 0.000000] gran_size: 64K chunk_size: 128K num_reg: 10 lose cover RAM: 38M Sep 4 09:43:16 t520sds kernel: [ 0.000000] gran_size: 64K chunk_size: 256K num_reg: 10 lose cover RAM: 38M Sep 4 09:43:16 t520sds kernel: [ 0.000000] gran_size: 64K chunk_size: 512K num_reg: 10 lose cover RAM: 38M Sep 4 09:43:16 t520sds kernel: [ 0.000000] gran_size: 64K chunk_size: 1M num_reg: 10 lose cover RAM: 38M Sep 4 09:43:16 t520sds kernel: [ 0.000000] gran_size: 64K chunk_size: 2M num_reg: 10 lose cover RAM: 38M Sep 4 09:43:16 t520sds kernel: [ 0.000000] gran_size: 64K chunk_size: 4M num_reg: 10 lose cover RAM: 38M Sep 4 09:43:16 t520sds kernel: [ 0.000000] gran_size: 64K chunk_size: 8M num_reg: 10 lose cover RAM: 38M Sep 4 09:43:16 t520sds kernel: [ 0.000000] gran_size: 64K chunk_size: 16M num_reg: 10 lose cover RAM: 38M Sep 4 09:43:16 t520sds kernel: [ 0.000000] *BAD*gran_size: 64K chunk_size: 32M num_reg: 10 lose cover RAM: -16M Sep 4 09:43:16 t520sds kernel: [ 0.000000] *BAD*gran_size: 64K chunk_size: 64M num_reg: 10 lose cover RAM: -16M Sep 4 09:43:16 t520sds kernel: [ 0.000000] gran_size: 64K chunk_size: 128M num_reg: 10 lose cover RAM: 0G Sep 4 09:43:16 t520sds kernel: [ 0.000000] gran_size: 64K chunk_size: 256M num_reg: 10 lose cover RAM: 0G Sep 4 09:43:16 t520sds kernel: [ 0.000000] gran_size: 64K chunk_size: 512M num_reg: 10 lose cover RAM: 0G Sep 4 09:43:16 t520sds kernel: [ 0.000000] gran_size: 64K chunk_size: 1G num_reg: 10 lose cover RAM: 0G Sep 4 09:43:16 t520sds kernel: [ 0.000000] *BAD*gran_size: 64K chunk_size: 2G num_reg: 10 lose cover RAM: -1G does this mean that my RAM is bad?! it also says Sep 4 09:43:16 t520sds kernel: [ 2.944123] EXT4-fs (sda1): INFO: recovery required on readonly filesystem Sep 4 09:43:16 t520sds kernel: [ 2.944126] EXT4-fs (sda1): write access will be enabled during recovery Sep 4 09:43:16 t520sds kernel: [ 3.088001] firewire_core: created device fw0: GUID f0def1ff8fbd7dff, S400 Sep 4 09:43:16 t520sds kernel: [ 8.929243] EXT4-fs (sda1): orphan cleanup on readonly fs Sep 4 09:43:16 t520sds kernel: [ 8.929249] EXT4-fs (sda1): ext4_orphan_cleanup: deleting unreferenced inode 658984 ... Sep 4 09:43:16 t520sds kernel: [ 9.343266] EXT4-fs (sda1): ext4_orphan_cleanup: deleting unreferenced inode 525343 Sep 4 09:43:16 t520sds kernel: [ 9.343270] EXT4-fs (sda1): 56 orphan inodes deleted Sep 4 09:43:16 t520sds kernel: [ 9.343271] EXT4-fs (sda1): recovery complete Sep 4 09:43:16 t520sds kernel: [ 9.645799] EXT4-fs (sda1): mounted filesystem with ordered data mode. Opts: (null) does this mean my HD is bad? As per FaultyHardware, I tried smartctl -l selftest, which uncovered no errors: smartctl 5.41 2011-06-09 r3365 [x86_64-linux-3.2.0-30-generic] (local build) Copyright (C) 2002-11 by Bruce Allen, http://smartmontools.sourceforge.net === START OF INFORMATION SECTION === Model Family: Seagate Momentus 7200.4 Device Model: ST9500420AS Serial Number: 5VJE81YK LU WWN Device Id: 5 000c50 0440defe3 Firmware Version: 0003LVM1 User Capacity: 500,107,862,016 bytes [500 GB] Sector Size: 512 bytes logical/physical Device is: In smartctl database [for details use: -P show] ATA Version is: 8 ATA Standard is: ATA-8-ACS revision 4 Local Time is: Mon Sep 10 16:40:04 2012 EDT SMART support is: Available - device has SMART capability. SMART support is: Enabled === START OF READ SMART DATA SECTION === SMART overall-health self-assessment test result: PASSED See vendor-specific Attribute list for marginal Attributes. General SMART Values: Offline data collection status: (0x82) Offline data collection activity was completed without error. Auto Offline Data Collection: Enabled. Self-test execution status: ( 0) The previous self-test routine completed without error or no self-test has ever been run. Total time to complete Offline data collection: ( 0) seconds. Offline data collection capabilities: (0x7b) SMART execute Offline immediate. Auto Offline data collection on/off support. Suspend Offline collection upon new command. Offline surface scan supported. Self-test supported. Conveyance Self-test supported. Selective Self-test supported. SMART capabilities: (0x0003) Saves SMART data before entering power-saving mode. Supports SMART auto save timer. Error logging capability: (0x01) Error logging supported. General Purpose Logging supported. Short self-test routine recommended polling time: ( 1) minutes. Extended self-test routine recommended polling time: ( 109) minutes. Conveyance self-test routine recommended polling time: ( 2) minutes. SCT capabilities: (0x103b) SCT Status supported. SCT Error Recovery Control supported. SCT Feature Control supported. SCT Data Table supported. SMART Attributes Data Structure revision number: 10 Vendor Specific SMART Attributes with Thresholds: ID# ATTRIBUTE_NAME FLAG VALUE WORST THRESH TYPE UPDATED WHEN_FAILED RAW_VALUE 1 Raw_Read_Error_Rate 0x000f 117 099 034 Pre-fail Always - 162843537 3 Spin_Up_Time 0x0003 100 100 000 Pre-fail Always - 0 4 Start_Stop_Count 0x0032 100 100 020 Old_age Always - 571 5 Reallocated_Sector_Ct 0x0033 100 100 036 Pre-fail Always - 0 7 Seek_Error_Rate 0x000f 069 060 030 Pre-fail Always - 17210154023 9 Power_On_Hours 0x0032 095 095 000 Old_age Always - 174362787320258 10 Spin_Retry_Count 0x0013 100 100 097 Pre-fail Always - 0 12 Power_Cycle_Count 0x0032 100 100 020 Old_age Always - 571 184 End-to-End_Error 0x0032 100 100 099 Old_age Always - 0 187 Reported_Uncorrect 0x0032 100 100 000 Old_age Always - 0 188 Command_Timeout 0x0032 100 100 000 Old_age Always - 1 189 High_Fly_Writes 0x003a 100 100 000 Old_age Always - 0 190 Airflow_Temperature_Cel 0x0022 061 043 045 Old_age Always In_the_past 39 (0 11 44 26) 191 G-Sense_Error_Rate 0x0032 100 100 000 Old_age Always - 84 192 Power-Off_Retract_Count 0x0032 100 100 000 Old_age Always - 20 193 Load_Cycle_Count 0x0032 099 099 000 Old_age Always - 2434 194 Temperature_Celsius 0x0022 039 057 000 Old_age Always - 39 (0 15 0 0) 195 Hardware_ECC_Recovered 0x001a 041 041 000 Old_age Always - 162843537 196 Reallocated_Event_Count 0x000f 095 095 030 Pre-fail Always - 4540 (61955, 0) 197 Current_Pending_Sector 0x0012 100 100 000 Old_age Always - 0 198 Offline_Uncorrectable 0x0010 100 100 000 Old_age Offline - 0 199 UDMA_CRC_Error_Count 0x003e 200 200 000 Old_age Always - 0 254 Free_Fall_Sensor 0x0032 100 100 000 Old_age Always - 0 SMART Error Log Version: 1 No Errors Logged SMART Self-test log structure revision number 1 Num Test_Description Status Remaining LifeTime(hours) LBA_of_first_error # 1 Extended offline Completed without error 00% 4545 - SMART Selective self-test log data structure revision number 1 SPAN MIN_LBA MAX_LBA CURRENT_TEST_STATUS 1 0 0 Not_testing 2 0 0 Not_testing 3 0 0 Not_testing 4 0 0 Not_testing 5 0 0 Not_testing Selective self-test flags (0x0): After scanning selected spans, do NOT read-scan remainder of disk. If Selective self-test is pending on power-up, resume after 0 minute delay. Googling for the messages proved inconclusive, I can't even figure out whether the messages are routine or catastrophic. So, what do I do now?

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• hp smart array lock up code 0x15, what is that? (or where can I get a list of descriptions of HP smart array controller lock up codes)

  - by user47650

  Hi, I've had a couple of Dl180 6g boxes hung over the last week, each have a P410 smart array controller. upon reboot the server has indicated that a controller failure event occurred and the previous lock up code was 0x15 - the server rebooted without issue. However there was nothing in the IML log, but the ADU report provided the following; Trap Address High Or Post Results Lockup Reason Or Post Error RIS Updates Or Post Error Detail Firmware Version Trap Address Low 0x8087 0x0015 0x0000033e 0x015e 0xd65c any suggestions on what that code is, my google fu failed. And hp support have not responded with any detail as yet.

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• How to Add Smart Tags to my .net component?

  - by Wael Dalloul

  look at the following picture, which showing smart tag for DataGridView Now I'm creating new component and I want it to support showing some properties in Smart Tags, how to add the properties to the smart Tag?

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• Declaring pointers; asterisk on the left or right of the space between the type and name?

  - by GenTiradentes

  I've seen mixed versions of this in a lot of code. (This applies to C and C++, by the way.) People seem to declare pointers in one of two ways, and I have no idea which one is correct, of if it even matters. The first way it to put the asterisk adjacent the type name, like so: someType* somePtr; The second way is to put the asterisk adjacent the name of the variable, like so: someType *somePtr; This has been driving me nuts for some time now. Is there any standard way of declaring pointers? Does it even matter how pointers are declared? I've used both declarations before, and I know that the compiler doesn't care which way it is. However, the fact that I've seen pointers declared in two different ways leads me to believe that there's a reason behind it. I'm curious if either method is more readable or logical in some way that I'm missing.

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