So I am now rewriting my fortran code in C (to use CUDA), and apparently I do not understand how to properly use malloc and pointers. I am trying to make the main function just calls to other functions, which need to malloc arrays that will then be used inside other functions. So, I am passing pointers of pointers to them as per this post: C Programming: malloc() inside another function
But the right amount of memory is not being allocated so I get segmentation faults. Here is the code:
#include <stdio.h>
#include <stdlib.h>
//#include <cuda.h>
#include <math.h>
//#include "cublas.h"
//datatype to match FORTRAN complex type
typedef float real;
typedef struct{
int nx;
int ny;
int nz;
int sz;
int tz;
} states;
void set_SPB(real **,int,states **,states **,int **);
//void set_SPB();
int find_minimum(int a[], int n,int start);
const real hc =197.32697,pi=3.1415927;
int main(){
int nmax = 2, A = 28;
real *etemp, *fock;
int *Ndex,*lookup,*lookup_a;
states *channel,*SPB;
//!generates the single particle basis to be used
set_SPB(&etemp,nmax,&SPB,&channel,&Ndex);
free(etemp);
free(Ndex);
free(SPB);
return 0;
}
void set_SPB(real **etemp,int nmax,states **SPB,states **channel,int **Ndex){
int tot_orbs = (2*nmax+1)*(2*nmax+1)*(2*nmax+1)*4;
int D = tot_orbs/4;
int Nalpha = (2*nmax+1)*(2*nmax+1)*(2*nmax+1)*9;
real E;
*etemp = (real*)malloc(D);
*Ndex = (int*)malloc(D*3);
*SPB = (states*)malloc(tot_orbs);
printf("orbits without spin degeneracy %d \n",D);
printf("size of etemp %ld \n",sizeof(*etemp)/sizeof(*etemp[0]));
return;
int i = 0;
for(int nx =-nmax;nx<=nmax;nx++){
for(int ny =-nmax;ny<=nmax;ny++){
for(int nz =-nmax;nz<=nmax;nz++){
E = 0.5*4.0*pi*pi*(nx*nx+ny*ny+nz*nz);
//printf("%d\n",i);
*etemp[i] = E;
*Ndex[0*D+i] =nx;
*Ndex[1*D+i] = ny;
*Ndex[2*D+i] = nz;
i+=1;
}
}
}
return;
}
Also I am not sure exactly if my assignments of the arrays are correct.
Specifically the print to find the number of elements of that have been allocated always gives 2, when it should be D = 125.
I cannot believe that float and int take only 1 byte in your environment.
Multiply the size to be allocated by size of their elements.
*etemp = malloc(sizeof(**etemp) * D);
*Ndex = malloc(sizeof(**Ndex) * D*3);
*SPB = malloc(sizeof(**SPB) * tot_orbs); /* not sure because this is not used */
Note that they say you shouldn't cast the result of malloc() in C.
Also note that [] operator has higher precedence than * operator, so you have to use parentheses to use the arrays.
(*etemp)[i] = E;
(*Ndex)[0*D+i] =nx;
(*Ndex)[1*D+i] = ny;
(*Ndex)[2*D+i] = nz;
Related
I need to have dynamic memory allocation without the use of malloc in an embedded application.
As we have enough RAM, I would like to allocate a big array (A[A_MAX]) on startup and have buffer arrays (B[]) within this one big array.
They would always begin at A[0] and be as long as they need (at max A_MAX, but mostly shorter).
Example:
at start up:
A[8] = {0,0,0,0,0,0,0,0};
declaring B[4] at A[0] and filling B with ones
B[4] = {1,1,1,1};
now A should look like this:
A[8] = {1,1,1,1,0,0,0,0}
How can I do this?
I looked at the sourcecode for malloc() and it does return the address of the next free part of the heap.
but when I use
float *B[4] = &A[0];
my compiler returns an error (invalid initializer)
As #neon mentioned I wanted to write an address to a float array.
Writing it like float *B = A[0] worked like a charm.
You may do:
#include <stdalign.h>
#define A_MAX 8
alignas(max_align_t) char _memory[A_MAX] = {0};
then you can just use pointers:
int main() {
{
float *floatdata = (void*)_memory;
// use floatdata
}
{
int *intdata = (void*)_memory;
// use intdata
}
}
I would write a handy function to calculate the maximum size for error checking:
// query the max size and allocate
inline void *dataalloc(size_t elemsize, size_t *n) {
*n = sizeof(_data) / elemsize;
return _data;
}
and do:
size_t size;
float *floatdata = dataalloc(sizeof(*floatdata), &size);
// use as-if floatdata[size]
for (size_t i = 0; i < size; ++i) floatdata[i] = i;
do you mean something like ? I'm using pointers to the array
#include <stdio.h>
#include <stdlib.h>
void allocator(float* src,int SrcSize,float **dst,int size,int pos){
if(size <= SrcSize)
for(int i=0;i<size;i++){
dst[i] = &(src+pos)[i];
}
}
int main()
{
float A[8] = {0,0,0,0,0,0,0,0};
float *B[4];
float *C[4];
allocator(A,sizeof(A)/sizeof(float),B,4,0);
*B[2] = 4;
allocator(A,sizeof(A)/sizeof(float),C,4,4);
*C[0] = 6;
printf("A[2] value is : %f\n" , A[2]); // output is 4.000
printf("A[4] value is : %f\n" , A[4]); // output is 6.000
return 0;
}
I'd like to use my own type matrix in C using a syntax matlab-like to access it. Is there a solution using the preprocessor? Thanks. (The following code doesn't work).
include <stdio.h>
#define array(i,j) array.p[i*array.nrows+j] //???????????
typedef struct
{
unsigned int nrows;
unsigned int ncols;
float* p;
} matrix;
int main()
{
unsigned int i=4,j=5;
float v=154;
matrix a;
a.p=(float*) malloc(10*sizeof(float));
array(i,j)=v;
return 0;
}
You would have to pass in the name of your array to the macro, but yes, you could do something like that.
Just as an FYI, MATLAB order is more generally known as "column major". C order is more generally known as "row major order".
I have taken the liberty of correcting 1) your memory allocation and 2) your initialization of the dimensions since they are necessary for the macro to work properly:
include <stdio.h>
#define INDEX(mat, i, j) (mat).p[(i) * (mat).nrows + (j)]
typedef struct
{
unsigned int nrows;
unsigned int ncols;
float *p;
} matrix;
int main()
{
unsigned int i = 4, j = 5;
float v = 154;
matrix a = {i, j, NULL};
a.p = malloc(i * j * sizeof(float));
INDEX(a, i - 1, j - 1) = v;
return 0;
}
Here the order is column major, but the index is still zero-based. I have highlighted this by accessing index [i - 1, j - 1] instead of [i, j]. If you want one-based indexing to really conform to MATLAB's way of doing things, you can change your macro to this:
#define INDEX(mat, i, j) (mat).p[((i) - 1) * (mat).nrows + (j) - 1]
Then in main, you could do:
INDEX(a, i, j) = v;
Maybe this approach could help you
#include <stdio.h>
#define array(arr,i,j) (arr.p[ i * arr.nrows + j ]) //???????????
typedef struct
{
unsigned int nrows;
unsigned int ncols;
float* p;
} matrix;
int main()
{
unsigned int i=4,j=5;
float v=154;
matrix a;
a.p=(float*) malloc(10*sizeof(float));
array(a,i,j)=v;
return 0;
}
If you will try to do: a(i,j) it will try to make a call to "a".
thank you for your help.
I fixed some trivial errors in the initial code.
I see your answers and I suppose that a matlab syntax cannot be implemented using a generic #define rule in the preprocessor for several structs.
Instead, a #define rule must be written for each specific struct as the following code.
Thank you so much again.
#include <stdio.h>
#define a(i,j) a.p[i*a.nrows+j]
typedef struct
{
unsigned int nrows;
unsigned int ncols;
float* p;
} matrix;
int main()
{
unsigned int i=4,j=5;
float v=154;
matrix a;
a.nrows=10;
a.ncols=10;
a.p=(float *) malloc(100*sizeof(float));
a(i,j)=v;
return 0;
}
I ran into this problem while working with a struct array within a struct. I'm trying to set the entry array in the dict using memcpy. I'm getting a mixture of the expected values and some seemingly random integers as output.
Oddly enough, I tried this code with some online compilers, and it worked fine. I thought that it might have to do with overlapping memory regions, so I tried memmove() but the result was the same.
I think I might be using malloc improperly for the dict, but I'm not sure. It seems I can't use malloc for the internal array, or for the individual elements. I'd appreciate any help.
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
typedef struct{
int i;
} entry;
typedef struct{
entry e[10];
int i;
} dict;
dict* d;
void test(dict* di){
printf("%d\n", di->i);
int k;
for (k = 0; k < 10; k ++){
printf(("%d\n"),di->e[k].i);
}
}
int main(){
entry en[10];
d = malloc(sizeof(d));
int k;
for (k = 0; k < 10; k++){
en[k].i = k;
}
d->i = 50;
memcpy(d->e, en, 10*sizeof(entry));
test(d);
return 0;
}
d = malloc(sizeof(d));
d is a dict*; sizeof d is sizeof(dict*). Looks like you meant sizeof *d.
I'm trying to make a struct that generates a random matrix and am getting "error: expected â=â, â,â, â;â, âasmâ or â_attribute_â before âmatrixâ" when compiling. How can I get this to work effectively and efficiently?
I guess expected errors usually are caused by typos but I don't see any.
I'm very new to C so pointers and malloc are quite foreign to me. I really appreciate your help.
/* It's called RandomMatrixMaker.c */
#include <stdio.h>
#include <stdlib.h>
typdef struct {
char* name;
int MID;
int MRows;
int MCols;
long[][]* MSpace;
} matrix;
matrix makeRIDMatrix(char* name, int MID, int MRows, int MCols) {
matrix m;
static int i, j, r;
m.name = name;
m.MID = MID;
m.MRows = MRows;
m.MCols = MCols;
for (i=0; i<m.MRows; i++) {
for (j=0; i<m.MCols; j++) {
r = random(101);
*(m.MSpace[i][j]) = r;
}
}
return m;
}
int main(void) {
makeRIDMatrix("test", 1, 10, 10);
return 0;
}
There is indeed a typo. You misspelled typedef:
typdef struct {
should be:
typedef struct {
EDIT:
Also, there's no reason to use static here:
static int i, j, r;
You can just get rid of the static modifier.
int i, j, r;
As another poster mentioned, there's a typo, but even with that corrected, it wouldn't compile, due to the definition of matrix.MSpace.
Let's begin in makeRIDMatrix(). You've declared an automatic (stack) variable of type "matrix". At the end of the function, you return that object. Whilst this is permissible, it's not advisable. If the struct is large, you will be copying a lot of data unnecessarily. Better to pass a pointer to a matrix into makeRIDMatrix(), and have makeRIDMatrix() fill in the contents.
The test in the inner loop is against i, but should be against j.
Next, let's look at the definition of "matrix". The definition of "MSpace" is a mess, and wouldn't even compile. Even if it did, because you haven't defined the length of a row, the compiler would not be able to calcuate the offset to any given item in the array. You want a two-dimensional array without giving the row length, but you can't do that in C. You can in other languages, but not C.
There's a lot more I could point out, but I'd be missing the real point. The real point is this:
C Is Not Java.
(It's also not one of the interpreted languages such as JavaScript, PHP, Python, Ruby and so on.)
You don't get dynamically-expanding arrays; you don't get automatic allocation of memory; you don't get garbage collection of unreferenced memory.
What you need is something more like this:
#include <stdio.h>
#include <stdlib.h>
#include <time.h>
typedef struct {
char* name;
int MID;
unsigned int MRows;
unsigned int MCols;
long *MSpace;
} matrix;
void makeRIDMatrix(matrix *pmx, char* name, int MID,
unsigned int MRows, unsigned int MCols) {
int i, j;
long *MSpace = malloc(sizeof(*MSpace)*MRows*MCols);
if (MSpace == NULL) {
return;
}
pmx->name = name;
pmx->MID = MID;
pmx->MRows = MRows;
pmx->MCols = MCols;
pmx->MSpace = MSpace;
srandom((unsigned int)time(NULL));
for (i=0; i<MRows; i++) {
for (j=0; i<MCols; j++) {
long int r = random() % 101L;
*(MSpace++) = r;
}
}
}
inline long * item_addr(const matrix *pmx,
unsigned int row, unsigned int col) {
if (pmx == NULL || pmx->MSpace == NULL
|| row >= pmx->MRows || col >= pmx->MCols) {
return NULL;
}
return &(pmx->MSpace[row * pmx->MCols + col]);
}
long get_item(const matrix *pmx, unsigned int row, unsigned int col) {
long *addr = item_addr(pmx, row, col);
return addr == NULL ? 0L : *addr;
}
void set_item(matrix *pmx,
unsigned int row, unsigned int col,
long val) {
long *addr = item_addr(pmx, row, col);
if (addr != NULL) {
*addr = val;
}
}
int main(void) {
matrix m;
makeRIDMatrix(&m, "test", 1, 10, 10);
return 0;
}
Note a few things here. Firstly, for efficiency, I fill the array as if it were one-dimensional. All subsequent get/set of array items should be done through the getter/setter functions, for safety.
Secondly, a hidden nasty: makeRIDMatrix() has used malloc() to allocate the memory - but it's going to be job of the calling function (or its successors) explciitly to free() the allocated pointer when it's finished with.
Thirdly, I've changed the rows/cols variables to unsigned int - there's little sense in definining an array with negative indices!
Fourthly: little error checking. For example, makeRIDMatrix() neither knows nor cares whether the parameter values are sensible (e.g. the matrix pointer isn't checked for NULLness). That's an exercise for the student.
Fifthly, I've fixed your random number usage - after a fashion. Another exercise for the student: why is the way I did it not good practice?
However - all of this is moot. You need to get yourself a good C textbook, or a good online course, and work through the examples. The code you've given here shows that you're punching above your weight at the moment, and you need to develop some more C muscles before going into that ring!
In relation to your question about "variable sized arrays", you could have something like:
/* can stick this into your struct, this is just an example */
size_t rows, cols;
long **matrix;
/* set the values of rows, cols */
/* create the "array" of rows (array of pointers to longs) */
matrix = (long**)malloc(rows * sizeof(long*));
/* create the array of columns (array of longs at each row) */
for (i = 0; i < rows; i++)
matrix[i] = (long*)malloc(cols * sizeof(long));
/* ... */
/* free the memory at the end */
for (i = 0; i < rows; i++)
free(matrix[i]);
free(matrix);
Then you can just access the dynamically allocated matrix similar to any other array of arrays.
ie. to set element at the first row (row 0) and fourth column (column 3) to 5:
matrix[0][3] = 5;
I am writing a C-program where I need 2D-arrays (dynamically allocated) with negative indices or where the index does not start at zero. So for an array[i][j] the row-index i should take values from e.g. 1 to 3 and the column-index j should take values from e.g. -1 to 9.
For this purpose I created the following program, here the variable columns_start is set to zero, so just the row-index is shifted and this works really fine.
But when I assign other values than zero to the variable columns_start, I get the message (from valgrind) that the command "free(array[i]);" is invalid.
So my questions are:
Why it is invalid to free the memory that I allocated just before?
How do I have to modify my program to shift the column-index?
Thank you for your help.
#include <stdio.h>
#include <stdlib.h>
main()
{
int **array, **array2;
int rows_end, rows_start, columns_end, columns_start, i, j;
rows_start = 1;
rows_end = 3;
columns_start = 0;
columns_end = 9;
array = malloc((rows_end-rows_start+1) * sizeof(int *));
for(i = 0; i <= (rows_end-rows_start); i++) {
array[i] = malloc((columns_end-columns_start+1) * sizeof(int));
}
array2 = array-rows_start; //shifting row-index
for(i = rows_start; i <= rows_end; i++) {
array2[i] = array[i-rows_start]-columns_start; //shifting column-index
}
for(i = rows_start; i <= rows_end; i++) {
for(j = columns_start; j <= columns_end; j++) {
array2[i][j] = i+j; //writing stuff into array
printf("%i %i %d\n",i, j, array2[i][j]);
}
}
for(i = 0; i <= (rows_end-rows_start); i++) {
free(array[i]);
}
free(array);
}
When you shift column indexes, you assign new values to original array of columns: in
array2[i] = array[i-rows_start]-columns_start;
array2[i] and array[i=rows_start] are the same memory cell as array2 is initialized with array-rows_start.
So deallocation of memory requires reverse shift. Try the following:
free(array[i] + columns_start);
IMHO, such modification of array indexes gives no benefit, while complicating program logic and leading to errors. Try to modify indexes on the fly in single loop.
#include <stdio.h>
#include <stdlib.h>
int main(void) {
int a[] = { -1, 41, 42, 43 };
int *b;//you will always read the data via this pointer
b = &a[1];// 1 is becoming the "zero pivot"
printf("zero: %d\n", b[0]);
printf("-1: %d\n", b[-1]);
return EXIT_SUCCESS;
}
If you don't need just a contiguous block, then you may be better off with hash tables instead.
As far as I can see, your free and malloc looks good. But your shifting doesn't make sense. Why don't you just add an offset in your array instead of using array2:
int maxNegValue = 10;
int myNegValue = -6;
array[x][myNegValue+maxNegValue] = ...;
this way, you're always in the positive range.
For malloc: you acquire (maxNegValue + maxPosValue) * sizeof(...)
Ok I understand now, that you need free(array.. + offset); even using your shifting stuff.. that's probably not what you want. If you don't need a very fast implementation I'd suggest to use a struct containing the offset and an array. Then create a function having this struct and x/y as arguments to allow access to the array.
I don't know why valgrind would complain about that free statement, but there seems to be a lot of pointer juggling going on so it doesn't surprise me that you get this problem in the first place. For instance, one thing which caught my eye is:
array2 = array-rows_start;
This will make array2[0] dereference memory which you didn't allocate. I fear it's just a matter of time until you get the offset calcuations wrong and run into this problem.
One one comment you wrote
but im my program I need a lot of these arrays with all different beginning indices, so I hope to find a more elegant solution instead of defining two offsets for every array.
I think I'd hide all this in a matrix helper struct (+ functions) so that you don't have to clutter your code with all the offsets. Consider this in some matrix.h header:
struct matrix; /* opaque type */
/* Allocates a matrix with the given dimensions, sample invocation might be:
*
* struct matrix *m;
* matrix_alloc( &m, -2, 14, -9, 33 );
*/
void matrix_alloc( struct matrix **m, int minRow, int maxRow, int minCol, int maxCol );
/* Releases resources allocated by the given matrix, e.g.:
*
* struct matrix *m;
* ...
* matrix_free( m );
*/
void matrix_free( struct matrix *m );
/* Get/Set the value of some elment in the matrix; takes logicaly (potentially negative)
* coordinates and translates them to zero-based coordinates internally, e.g.:
*
* struct matrix *m;
* ...
* int val = matrix_get( m, 9, -7 );
*/
int matrix_get( struct matrix *m, int row, int col );
void matrix_set( struct matrix *m, int row, int col, int val );
And here's how an implementation might look like (this would be matrix.c):
struct matrix {
int minRow, maxRow, minCol, maxCol;
int **elem;
};
void matrix_alloc( struct matrix **m, int minCol, int maxCol, int minRow, int maxRow ) {
int numRows = maxRow - minRow;
int numCols = maxCol - minCol;
*m = malloc( sizeof( struct matrix ) );
*elem = malloc( numRows * sizeof( *elem ) );
for ( int i = 0; i < numRows; ++i )
*elem = malloc( numCols * sizeof( int ) );
/* setting other fields of the matrix omitted for brevity */
}
void matrix_free( struct matrix *m ) {
/* omitted for brevity */
}
int matrix_get( struct matrix *m, int col, int row ) {
return m->elem[row - m->minRow][col - m->minCol];
}
void matrix_set( struct matrix *m, int col, int row, int val ) {
m->elem[row - m->minRow][col - m->minCol] = val;
}
This way you only need to get this stuff right once, in a central place. The rest of your program doesn't have to deal with raw arrays but rather the struct matrix type.