I was wondering why, in C, the sizeof of a struct is larger than the the sum of all the sizeofs of it's members. It only seems to be by a few bytes, but as a bit of a perfectionist I fine this a bit annoying.
View 1 RepliesWhy the size of a process grows larger in size for lots of small memory allocations. For example, say I have this struct, which is 16 bytes (for a 32 bit build):
Code:
struct Person {
int iID;
int iAge;
char * pForeName;
char * pSurName;
};
If I allocate memory like this:
Code:
LPBYTE lpB = new BYTE[sizeof(Person) * 1000000];
Then my process grows to 16,48KB in size, which is what I expected. However if I allocate memory like this:
Code:
Person * lpPerson;
for(int i = 0; i < 1000000; ++i)
lpPerson = new Person;
Then the process grows to 78,656KB, which I don't understand.
Additionally, I was surprised to find a vector acts more similarly to the first example. This code:
Code:
Person temp = { 0 };
std::vector<Person> people;
for(int i = 0; i < 1000000; ++i)
people.push_back(temp);
Only increases the process memory to 16,892.
#include <stdio.h>
#define MAX_USERS 20
struct {
char ID[10];
char Name[40];
int Pos;
[Code] .....
I was attempting something weired with address to move data around when I discovered that the size of the array is not what I expected. I am passing this structure as &Users to a function that declares it as a void *, then I can deal with chunks of data (memmove) and not have to worry about index or things like that. However...sizeof is returning something I do not understand.
Is it generally better to initialize string data members as nullptr or as a zero-size array?
I can understand the former is superior from a memory-use perspective and also not requiring the extra allocation step. However, many string management functions will throw an exception - wcslen for instance - if you pass them a null pointer. Therefore I am finding any performance gained is somewhat wiped out by the extra if(pstString==nullptr) guards I have to use where it is possible a wchar_* may still be at null when the function is called.
I'm having trouble figuring out how to find the size of an array program that involves "struct."
#include <iostream>
using namespace std;
struct d{
char* a;
float b;
int c;
[code].....
When I run this program, the output is 80(for my compiler). That would mean that each element in the array is 16 bytes but I don't understand how struct d is 16 bytes.
typedef struct Element Element;
struct Element {
char x;
double* y;
[Code] .....
This one with y pointer gives 8
typedef struct Element Element;
struct Element {
char x;
double y;
[Code] ....
This one with a normal y variable gives 12
Change the frame window size according to font size increases.
View 3 Replies View RelatedThe WinAPI has a struct like this for raw input:
Code:
typedef struct tagRAWINPUT { RAWINPUTHEADER header;
union {
RAWMOUSE mouse;
RAWKEYBOARD keyboard;
RAWHID hid;
} data;
[code]...
The definition of the struct doesn't show it but the documentation says that bRawData is variable length. sizeof(RAWINPUT) will not be the correct size when the data field is of RAWHID type so how do you allocate a variable with automatic storage type that has the right size for the entire struct? You can get a header that has the size for the entire struct but how do you actually allocate storage space for the data without using malloc? I've seen some example code that used a char array but that violates aliasing rules and there are also alignment issues with that approach.
I must take an old MFC project in VC++ 6.0 and make changes.
The problem is text size in screen is different from size in print preview.
for example with this font
Code:
CFont f50;
f50.CreateFont(100,0,0,0,FW_BOLD,0,0,0,DEFAULT_CHARSET,OUT_DEFAULT_PRECIS,
CLIP_DEFAULT_PRECIS,DEFAULT_QUALITY,FF_DONTCARE,"Frutiger LT Std 45 Light");
And this text
Code:
s=_T("Let's try to calculate the size of this text");
and with MM_LOMETRIC map mode
GetTextExtent() returns me:
On screen: (1595,99)
Ink printer + print preview: (1589,100)
PDFCreator + print preview: (1580,100)
comparing with screen size the height is bigger but lenght is smaller. I don't understand.
I can understand that different printers process the fonts in different way and then to have different lenghts. That's not the problem. The problem is I need to simulate in screen the same behaviour i will have on printer because these texts are being aligned in the document, and I don't want to see that the text si aligned different in text than in paper.
What can I do to render the text on screen with the same size I will have on the printer? Print preview is doing it. Should I change the font parameters? is something related with pixels per inch?
I'd wrote a program to encrypt a message within a bmp file using my own structs and all for everything (yes, call me a ........head) The program works but for some weird ........ing reason I was forced to subtract 2 bytes from the header size to get the correct value. I've narrowed down the issue to my BmpFileHeader struct.
Here's a short program that demonstrates the issue:
Code:
#include <stdio.h>
#include <stdlib.h>
#define BYTE unsigned char
#define WORD unsigned short
#define DWORD unsigned long
#define LONG signed int
[Code] .....
Tried with both gcc and TinyCC and got the same result so it doesent seem to be a compiler bug. Microsoft's structures though are giving the correct size, even though they have the exact same definition.
Microsoft's defines:
Code:
// windef.h
typedef unsigned long DWORD;
typedef unsigned char BYTE;
typedef unsigned short WORD;
[Code] .....
Suppose I have a struct with 20 members. I want to assign each of those structs with values. Instead of accesing by explicit convention, i.e.:
Code: struct.member1 = 1;
struct.member2 = 2;
...
...
...
struct.member20 = 6;
Is there any way to encapsulate it in a for loop and use an iterator variable to indicate the member? i.e.:
Code: for (int i = 0; i < 20; i++)
struct.i = i;
The above is pseudocode but Im sure you get what Im trying to do?
I am trying to pass multiple args to g_signal_connect through a struct and it's members. I think the problem lies with execlp. I am trying to pass the struct members to it but I keep getting errors. No matter how I format execlp and the struct args, I always get an error. The current error I receive is Bad address. Like I have said before, no matter how I format execlp, I receive some sort of error.
Code: /*
Compile me with:
gcc -Wall sshfs-gtk -o sshfs-gtk `pkg-config --cflags --libs gtk+-2.0`
*/
#include <gtk/gtk.h>
#include <string.h>
#include <stdlib.h>
#include <unistd.h>
#include <wchar.h>
static void destroy( GtkWidget *widget, gpointer data ) {
[Code] .....
If I have a struct of some vector members, like
struct {
vector<double> a;
vector<double> b;
vector<double> c;
// ...... continue
} struct_test
How can I assign a value (push_back()) to all the vector members simultaneously, instead of do it one by one?
I've been reading the tutorials on Friendship and Inheritance [URL] ..... but I still don't understand why I can't access members of the same struct type.
bool wordBeginsAt (int pos) {
if (pos == 0)
return true;
///use the 'message' string
Message go;
return isAlphanumeric(go.messageText[pos]) && (!isAlphanumeric(go.messageText[pos-1]));
}
The code above is located in a source file, where the function isAlphanumeric passes a char value, and Message is the struct containing the string I want to access. Below is the declaration of the struct and string located in the corresponding header file.
struct Message{
.
.
.
private:
std::string messageText;
};
My frustration comes when I try to call and assign messageText like the tutorial does to its private members, but I keep getting an error saying I can't access the string because it is a private member. Is there a way to access the string without having to pass it through the function wordBeginsAt?
I need to create a list of all members of a struct using the sturct definition as input. The struct is NOT part of the program, but is the input to the program.
The struct that I am using changes over time as features are added. I need the complete, fully qualified field names to then generate a table with all names with their offsets, type and length.
This information then allows me to create readers of the data that will run on different architectures, compilers and operating systems.
The struct currently has 800+ lines and uses typedef and embedded structs.
Perhaps this could be done creating LEX, YACC, Perl, SED, AWK or other language system.
I've been looking into the file structure of BMP images and everything I'm reading says that the 4 bytes following the signature are designated as the filesize of the bmp file... It's always zero for me regardless of the BMP file. The signature is always correct though.
Code:
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <errno.h>
#include <stdint.h>
[Code]....
I'm trying to put all of the words in a text document into an array but this text document is 2,138 kb, and when my program is crashing when I try to put it into an string array. Could the file be too big to put into the array?
View 2 Replies View RelatedThe problem is with that a. What is it, a pointer? What's the difference between the a in the main function and the a in the function?
#include <iostream>
#include "Header.h"
using namespace std;
short int capacity(int* a) {
int capacity;
[Code] ....
The function it returns i think the size of the pointer instead of returning the size of my array. I don't think i fully understood pointer arithmetic.
How can I see the actual byte size of the pointer as output in the command prompt?
#include <iostream>
using namespace std;
int main () {
[Code].....
Here is what I've tried:
int numbers[] = {8, 2, 0, 4, 100, 5};
for(int i = 0; i < sizeof(numbers); i++){
cout << numbers[i] << endl;
}
However the results in the console is: 8 2 0 4 ,What am I doing wrong? Am I using the wrong built in function or something? I googled this and one of the links that came up stated to just do something like
arrayName.size()
but that didnt work for me either...
[URL]
Also, I know that I just enter the size of the list manually, in this case make i < 6 but I still want to know if there is a built in function or something.
what is the size of integer in dos?
View 2 Replies View Relatedhow am i supposed to alter font size of text which appear in output screen?
View 1 Replies View RelatedI am not sure why I am receiving the error message:
Error C2466: cannot allocate an array of constant size 0
When I run the code:
Code:
int s;
cout<<"Enter the size:
";
cin>>s;
int array[s];
C++ masters,
I have this simple program:
Code:
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
static unsigned char cmd[]={
0x01,0x80,0x00,0x00,0x00
[Code] .....
All is right except the size. Why does it give 80x1 as size instead of the digit 5?
I want to find the size of the data type with out using sizeof() operator.
View 9 Replies View RelatedAfter looking online for a string replace function in C and finding so many examples that go through the entire string twice. First round to find how number of occurances of substitute in string, using that to malloc for a new string to include additional space for replace, then going through the search string again to get all but what's to be substituted out. I feel it's kind of silly to go through the string twice. Therefore, I'm trying to implement my own string replace, that only searches through the string for what's to be substituted, once.
Here is my code:
Code:
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
char *strreplace(char * string, char * sub, char * replace);
}
[code]....
Here is the same code, but with execution + some syntax highlighting: Ideone.com | Online C Compiler & Debugging Tool..It works great, until it gets to grabbing whatever remains in the search string after the last found sub. The realloc throws a runtime error:
Code:
*** glibc detected *** ./a.out: realloc(): invalid next size: 0x00011008 ***
Aborted From my understanding, this is from me going outside of the bounds of the heap and using memory I haven't allocated, or using a free'd pointer. I'm not seeing where either of these are happening in my code, and was wondering what the best way to go about figuring out where the error exactly occurs.