Why the output file isn't the same as the input of the variable?

Question

I create it a program that asks for raw and columns after that asks you to put numbers to the dimensional array. This arrays inputs to a file. When i open the file i can't see the array.

#include <stdio.h>
#include <stdlib.h> 
#include <curses.h>

int main () {
FILE *fp;
int n,m;
int i,j;
float b;
char filename[100];
int getfloat(float *);

printf("Number of rows\n");
scanf("%d",&n);
printf("Number of colums\n");
scanf("%d",&m);
float s[n][m];

for (i=1;i<=n;i++)
{
   for (j=1;j<=m;++j) 
   {
       printf("Insert number %d",i);
       printf(",%d\n", j);
       scanf("%f",&b);
       s[i][j]=b;
    }
}          

printf("Enter file name \n");
scanf("%s", filename);

// ****print file****
fp=fopen(filename,"w+");
if(fp!=NULL)
{
   fputs(s,fp);
   fprintf("%c",s);
}
fclose(fp);

return 0;

the only thing i see is this

Invalid Characters

`fputs` writes a C-string (an array of chars terminated by a NULL character) (see [here](http://www.cplusplus.com/reference/cstdio/fputs/). Also see [some books](https://stackoverflow.com/questions/562303/the-definitive-c-book-guide-and-list). Also, arrays are indexed from 0 to N-1 (N being the size of the array). — Phil M, Mar 29 '19 at 16:04
The fix to your code depends on how you want the data stored in the file. Are you looking for a series of binary representations of the floats, or are you looking for a human-readable list of values? — Phil M, Mar 29 '19 at 16:08

score 2 · Accepted Answer · answered Mar 29 '19 at 16:14

2

If you want a list of numbers, probably in some kind of grid in the file, then at the minimum you want a loop such as the following:

for (int i=0; i<n; ++i)
{
    for (int j=0; j<m; ++j)
    {
        fprintf(fp, "%f ", s[i][j]);
    }
    fprintf(fp, "\n");
}

See fprintf for documentation on the format specifiers; you'll probably want to tweak that to get better-looking values.

Also, again, note that arrays start from 0. Your initial read loop skips the very first element, and writes past the end of the actual array.

answered Mar 29 '19 at 16:14

Phil M

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Thanks a lot that help me but i dont also need this lines fp = fopen(filename, "wb"); fwrite(s,sizeof(float),sizeof(s),fp); fclose(fp); – Dan Boutsi Mar 29 '19 at 16:24
I just show the loop, assuming you've opened the file, and close it after. You can use other `fprintf` statements before the loops if you need to write out the dimensions of the array, but `fwrite` is going to write binary data, which it doesn't sound like you want. – Phil M Mar 29 '19 at 16:27
@DanBoutsi: You would use `fwrite` if you wanted to store the *binary* (not human-readable) representation of the array. If you opened that file in a text editor you'd see a sludge of garbage characters, not a nicely-formatted grid of numbers. – John Bode Mar 29 '19 at 17:24

score 0 · Answer 2 · answered Mar 29 '19 at 16:14

fprintf("%c", s); and fputs does not print out the contents of the array, it prints out the location stored in the array's pointer and tries to interpret it as a char. What you would need to print out the proper values is to loop through each value and use fprintf with each float value, using s[i][j] similar to how you initialized it.

The way you initialized the array is also off, as arrays begin at 0, not 1. Currently your for loop does not ever access s[0][0] or s[1][0] and so on. Your for loops should have i initialized to 0, and have the condition be i < n instead of i<=n.

Why the output file isn't the same as the input of the variable?

2 Answers2