C++ :: Does Realloc To Smaller Memory Result In Same Pointer
Aug 10, 2014
If I do this:
void* testPtr = malloc ( 1000 )
And then this:
testPtr = realloc ( testPtr, 500 )
Will the realloc just reduce the allocated size and keep the same pointer, or can there be a chance of it finding another place for that allocation ( Meaning that it will expensively move the memory to another location )?
I am trying to create efficient programs by making my dynamic allocations the least resource hungry as possible during runtime.
The results of my code is supposed to be very simple: return the 2 integers and then their sum. However, it's doing returning the first value, then an address in memory(rather than the 2nd value), and then the 2nd value(rather than the sum). Here is the code:
what's the ideal way to get an iterator to the item that has the largest key (int) smaller than a given value.
basically, the item before upper_bound(). I can use upper_bound() and then decrement, but it needs special cases for both end() and begin(), and in the case of end() I'm not sure how I get it to the last item in the map, afaik, we're not allowed to decrement end().
Code: auto it = mymap.upper_bound(x); if (it==mymap.begin()) // first item in the map is already too large. reject NotFound(); else if (it==mymap.end())
[Code] .....
// here it points to largest item smaller than x.
I can iterate over the entire map and do a compare, but then I pretty much loose the benefit of the binary search.
I have a large binary file (84GB) that needs to be broken down into smaller file sizes (~1GB to 8GB) for analysis. The binary file is on a 32-bit machine and cannot be copied to another machine for analysis. The PC has Visual Studio 6.0 and is not upgradable. My issue is I'm using the following generic code to create the smaller files.
fseek(file, start, SEEK_SET); end = start + (variable based on file size); fseek(file, end, SEEK_SET); for (i=start; i<end; i++) { if(!feof(f)) { byte = fgetc(f); fputc(byte,new_file); } }
However, on a 32-bit machine, the iterator can only count up to ~2billion. Which means that I'm unable to copy anything past ~2GB. My original idea was to delete from the large binary file as I read from it so that I can reset the iterator on every read. However, I haven't come across a way to delete binary file entries.
Is there any other way that to break down a large binary file into smaller units? Or is there a way to delete binary file entries in sections or per entry?
On a 64-bit machine I could use _fseeki64. I've been reading that some versions of Visual 6.0 are capable of supporting 64-bit numbers but when using _fseeki64 or _lseeki64 on this machine its an "undeclared identifier"
I wrote the following C++ constructor, and I get an error - BUFFER too small on strcpy_s
Trace::Trace(const char *str) { if (str) { int len = strlen(str); this->m_name = new char[len+1]; // asking for 'len+1' memory elements of char strcpy_s(m_name, len, str); // **** I get here an error "BUFFER TOO SMALL" ****
i want to improve my knowledge about the dyn allocation of char pointers... with this code i wanted to type a string and insert the string in a array created dynamically:
Code:
#include <stdio.h> #include <stdlib.h> #include <string.h> int main() { char c; char *test=NULL; unsigned int len; }
[code]....
why there are these 3 initial character '' ')' ':' that i didn't have typed...
I would like to realloc a 2D array. I have a counter, itime, it increases each step. Each step, I would like to reallocate my array, keeping the old values, and add new values to the array. When itime=1, I use only malloc, because it is allocated for the first time. When itime increases (e.q. itime=2), realloc comes into process. In the realloc process the GUI crashes.
I'm working with memory mapped files and I have a block of memory that I've mapped to.
I want to write a function that returns a pointer to a portion of the mapped memory at an offset and length so I can write to it. I've never worked with memory at this level, is what I'm attempting possible?
I know that mapping functions can map to a part of the file at length and offset but I'm not sure if I should make multiple calls to map the memory from the file or just map the memory once and work with the portions I'm interested in using my proposed GetMemory function.
Code:
LPVOID m_lpData; LPVOID GetMemory(DWORD pos, DWORD length) { BYTE* buffer = (BYTE*)m_lpData; buffer += pos; // how to get a length of the memory? return ((LPVOID)buffer); }
I am using a pair of pthreads that call a pair of functions for ping-pong dma data transfer that are used in a loop for data transfer from an acquisition board. For a large # of waveforms, I ultimately run out of PC memory and the program stops. At the end of each function I use the delete[] command to clear memory for reuse, but the pointer appears to advance by the array size used for the transfer until the location exceeds the 2 GB I have for memory. I can see this happening using the Task Manager performance button time plot and window of total memory used continuing to increase to the limit. The culprit for one of the functions (2nd) is:
where pci_buffer1 and 2 have been set up and allocated in main. I also had the following line in each function process:
double* Rin = new double[length];
and it used up memory twice as fast. When I transferred the last line to an area just prior to main and used a constant 1024 for length, the program ran twice as far before exceeding system memory, so it appears that both lines were forcing new memory assignments and moving the pointers accordingly. In addition to using the delete[] command to free memory unsucessfuly at the end of each function procedure, I ended up closing the memory at the end of each procedure, then reallocating it again with the idea that the pointer would be set back to the original value, but it still seems to icrement along. So, neither approach appears to allow reuse of the memory because the pointer continues to march along. Using Visual C++ 6.0 to compile.
When I make a shallow copy of pMeshData to OriginalMesh (for static mesh rendering, 2 objects pointing to one COM interface), memory leaks start to occur.When I don't, everything is fine.How to solve it? I addref() to it once (with pMeshData) and ReleaseCOM it in destroyMeshContainer
Remarks **** MeshData.pMesh is 0x00000000 while OriginalMesh is a pointer of some value whose values are 0xfeeefeee
how to correctly use realloc on an array of char arrays? Say I want to store strings in arrays (=array of char arrays) and double the size of max. strings (y value):
Code:
int x=200; int y=10; char *carray[y]; for (int j = 0; j < y; ++j) carray [j] = malloc (sizeof(char)*x);} }
An attempt to create a class which is basically a mimic of vector<int> i don't seem to know how to delete pointer x in a destructor to free memory, also on pushback and pushfront methods, i can't free y when i implement delete[] y; y=NULL; i get some NULL out put when cout 'ing the object in main, why is that happening and how do i free memory y.
#include<iostream> using namespace std; class vectorOfint{ int* x; int size; public: vectorOfint();
I have found that when I dump a C++ object from memory to a file - it seems that there is a misplacement of the last Virtual-Function-Table pointer - in that appears at the beginning. The result is that the gdump information based on this object dump (using green hills) is incorrect. I copied the contents of the gdump information below. The executable is compiled in linux.
Basically MEIO::CameraStatus contains an item that relates to its parent class (line 188). Then it has 18 items that are all Diagnostics::EventsCounter items. Now for each Diagnostics::EventsCounter item there is a Virtual-Function-Table Info Pointer as its last item. All is fine and good except that the last item of MEIO::CameraStatus which is _selfReset is missing its last item of 4 bytes (which is the Virtual-Function-Table Info Pointer ). On the other hand - right before the first Diagnostics::EventsCounter item ("_vidErrors") - there is an extra 4 bytes which happens to be the Virtual-Function-Table Info Pointer. As I said the gdump information file does not see this.
Why the object memory "moves" the last Virtual-Function-Table Info Pointer to the beginning (right before _vidErrors) and is there a way to "fix" this?
/////////////////////////////////////////////////////////////////////////// "MEIO::CameraStatus" val:0x000002f0 ind208,-1) Struct-Begin Info 188: "" offset 0, Parent-Class Private Info C++ Struct ref = 114 189: "_vidErrors" offset 160, Member Info C++ Struct ref = 128 190: "_vdiErrors" offset 480, Member Info C++ Struct ref = 128
I'm trying to keep track of the size of blocks of memory that a pointer points to. No matter what I do, this code below always outputs the integer 8.
If I change 1000 to 5, I still get 8. If I change it to 0, I get 8... If I change it to -1, I get 8. If I change int *a to double *a, I get 8. If I take away the & symbol, I get 8. If I use *& instead, I get 8.
Why? I want it to output 1000. If I change that to 500, I want it to output 500.
int *a; a = malloc(1000 * sizeof(int));
int j = sizeof(&a); printf("%d", j);
I want to build my skills where I can allocate, inspect and change memory sizes.
If I have a pointer variable indicating memory location in which we have stored what user entered and the pointer is of type volatile if the user gives the character 'a' twice , then this character will not be fetched twice from the memory but only when the character is changed???
This is the one meaning of the volatile? the other is that the value will be changed without the program itself change it?
Info:Program that stores information about reports .the above function searches the report according to its title. list is the name of the structure that stores the records.
Why i'm using strstr:
for eg. there is a report titled 'report on tigers'
I want the report information to be output if someone searches for 'tiger'
Output:displays all the entries i have made till now
I'm trying to understand the pass by value-result. The code I have came up with so far only does by value and by reference, which I understand. The value-result is what has me stumped, and honestly I am unsure how to write the function for it. Here's my code so far...
#include <iostream> using namespace std; // Function prototypes. void swapByValue(int, int, int); void swapByRef(int&, int&, int&);
I keep getting an undesired value in this code. I've tried several methods, but none are giving me the correct answer. The out put is always zero, when in this case it should be 10!!
Here's the object structure:
template<class T, class _b> struct quantity { private: T value; public: explicit quantity(T val): value(val) {}; T getValue() { return value; };
Why does it seem that the assignment operator is the harder operator to overload? Maybe it's just my luck, but I seem to always run into issues whenever I work with it. I hardly ever experience errors when overloading any of the other operators.
I am trying to make the code below display the result with decimals. I tried using setprecision, but I am not too sure where to put it. I placed it in cout section where the answer is but it still doesn't come out correctly.
#include <iostream> using namespace std; //*Delcare function prototype* int ConvertToCentimeters (double, double ); //declare exception class* class NegativeNumber
