C / C++ / MFC

Victor Nijegorodov wrote:

Shouldn't it be

C++

data = (double *) malloc(num_cols * sizeof(double*));

data = (double **)malloc(num_cols * sizeof(double *));

data = (double **)malloc(num_cols * sizeof *data);

leon de boer wrote:

Lets list the ones I know that don't have a c++ compiler

Quote:

$ mpicc gaussian.c
gaussian.c: In function ‘main’:
gaussian.c:73:8: warning: assignment from incompatible pointer type [-Wincompatible-pointer-types]
data = (double *) malloc(num_cols * sizeof(double *));
^
$

data = (double **) malloc(num_cols * sizeof(double **));
 /*???? data = new double*[num_cols];*/


 for(int i = 0; i < num_cols; i++)
 data[i] = (double *) malloc(num_rows * sizeof(double));

/* First you malloc a set of pointers to a double ... not a pointer to a pointer to a double */ 
/* data is a pointer to a pointer of double .. so you need to allocate pointers to doubles */
data = (double **) malloc(num_cols * sizeof(double *));

/* Then for each pointer of double you malloc a 1D array of doubles to that pointer */
for(int i = 0; i < num_cols; i++)
  data[i] = (double *) malloc(num_rows * sizeof(double));

/* see how the thing inside the sizeof is always one asterix less than what malloc returns */

double* data1D = (double*) malloc(num_rows * num_cols * sizeof(double));

data[i][j]

data1D[j*num_cols + i]

ChrisFromWales wrote:

The last version of cfront was released around the time that the C++ language added templates
[...]
cfront version 3.0.3 from May 1994 [...]

Quote:

The purpose of this Task is to let you express your problem-solving skills, programing skills, as well as to reveal your style of coding.

int *file_buffer = malloc(num_rows * sizeof(int)); // assumes you are reading ints from file

//C++ 

  send_buffer = new double[num_rows];

send_buffer = (double *)malloc(num_rows * sizeof(double);

zak100 wrote:

Please let me know.

void *calloc(size_t nitems, size_t size)

send_buffer = (double *)calloc(num_rows, sizeof(double));

Preprocessor are executed before compilation. This is a macro processor, which is used automatically by the C compiler to transform your program before actual compilation.

In simple words, preprocessor directives tells the compiler to preprocess the source code before compiling. All the preprocessor commands are begin with "#" symbol.

The most common use of the preprocessor is to include header files. In C and C++, all symbols must be declared in a file before they can used. They don’t always need to be defined*, but the compiler needs to know they exist somewhere. A preprocessor is just another technique to help a programming language be more useful. There are numerous techniques available and every language designer must choose the ones they like.