Re: Whaddaya think?

On 6/25/2024 1:37 PM, Lew Pitcher wrote:

On Sun, 16 Jun 2024 15:52:16 +0000, Lew Pitcher wrote:
 

On Sat, 15 Jun 2024 15:36:22 -0400, DFS wrote:
>

I want to read numbers in from a file, say:
>
47 185 99 74 202 118 78 203 264 207 19 17 34 167 148 54 297 271 118 245
294 188 140 134 251 188 236 160 48 189 228 94 74 27 168 275 144 245 178
108 152 197 125 185 63 272 239 60 242 56 4 235 244 144 69 195 32 4 54 79
193 282 173 267 8 40 241 152 285 119 259 136 15 83 21 78 55 259 137 297
15 141 232 259 285 300 153 16 4 207 95 197 188 267 164 195 7 104 47 291
>
>
This code:
1 opens the file
2 fscanf thru the file to count the number of data points
3 allocate memory
4 rewind and fscanf again to add the data to the int array
>
>

[snip]

You /could/ create a temporary, binary, file, and write the fscanf()'ed
values to it as part of the first loop. Once the first loop completes,
you rewind this temporary file, and load your integer array by reading
the (now converted to native integer format) values from that file.
>
Still two passes, but using fscanf() in only one of those passes.

[snip]
 For what it's worth, here's an example of what I suggest:
 /*
The following code provides two examples of the approach I suggested.
 Example 1: while counting input numbers, write temp file with int values
   malloc() a buffer big enough for that count of int values
   fread() the temp file into the malloc()'ed buffer
   Note: conformant to ISO Standard C.
 Example 2: while counting input numbers, write temp file with int values
   mmap() the temp file, starting at the beginning, and sized to
   include all the int values in the file.
   Note: conformant to POSIX C extensions to ISO Standard C.
 Note: compile with -DUSE_MMAP to obtain mmap() variant, otherwise
       this will compile the malloc()/fread() variant
*/
 #include <stdio.h>
#include <stdlib.h>
 #ifdef USE_MMAP
   #include <sys/mman.h>
   #define BANNER "Example of array loading using mmap()"
   #define FREEALLOC(x)
#else
   #define BANNER "Example of array loading using malloc() and fread()"
   #define FREEALLOC(x) free((x))
#endif
 static int *LoadIntArray(FILE *fp, size_t *Count);
 int main(void)
{
   int status = EXIT_FAILURE, *array;
   size_t count;
    puts(BANNER);
    if ((array = LoadIntArray(stdin,&count)))
   {
     printf("%zu elements loaded\n",count);
     for (size_t index = 0; index < count; ++index)
       printf("array[%3zu] == %d\n",index,array[index]);
      FREEALLOC(array); /* if necessary, free() the malloc()'ed array */
     status = EXIT_SUCCESS;
   }
   return status;
}
 static int *LoadIntArray(FILE *fp,size_t *Count)
{
   FILE *tmp;
   int *array = NULL;
   size_t count = 0;
    if ((tmp = tmpfile()))
   {
     int buffer;
      for (count = 0; fscanf(fp,"%d",&buffer) == 1; ++count)
       fwrite(&buffer,sizeof buffer, 1,tmp);
      if (count)
     {
#ifdef USE_MMAP
       /*
       ** USE mmap() to map temp_file data into process memory
       */
       array = mmap(NULL,
                    count * sizeof *array,
                    PROT_READ,MAP_PRIVATE,
                    fileno(tmp),
                    0);
       if (array == MAP_FAILED)
       {
array = NULL;
fprintf(stderr,"FAIL: Cannot mmap %zu element array\n",count);
       }
#else
       /*
       ** USE malloc() to reserve a big enough heap-space buffer,
       ** then fread() the temp_file data into that buffer
       */
       if ((array = malloc(count * sizeof *array)))
       {
rewind(tmp);
if (fread(array,sizeof *array,count,tmp) != count)
{
  free(array);
  array = NULL;
  fprintf(stderr,"FAIL: Cannot load %zu element array\n",count);
}
       }
       else fprintf(stderr,"FAIL: Cant malloc() %zu element array\n",count);
#endif
     }
     fclose(tmp);
    }
   else fprintf(stderr,"FAIL: Cannot allocate temporary work file\n");
    *Count = count; /* byproduct value that caller might find useful */
   return array; /* either NULL (on failure) or pointer to array */
}
 

$ gcc -Wall LewPitcher_readnums.c -o lprn
$ (no compile errors)
$ ./lprn nums.txt
Example of array loading using malloc() and fread()
(then it just hung)
$ gcc -Wall LewPitcher_readnums.c -o lprn -DUSE_MMAP
$ (no compile errors)
$ ./lprn nums.txt
Example of array loading using mmap()
(then it just hung)
Am I supposed to hardcode the filename in there somewhere?