Short int - how to save to the file

Question

I have unsigned short int (from 0 to 65535) and I must save it to the file, using stdio and consuming 2 bytes, but I don't know, how.

Any suggestions?

Errata · Answer 1 · 2011-03-14T08:55:28.720

2

I will use an union (yeah I dislike using cast..) :

template <typename T>
union Chunk {
  T _val;
  char _data[sizeof(T)];
};

int main(void) {
   std::ofstream output;
   Chunk<short> num;
   num._val = 42;
   output.open("filepath.txt");
   if (output.good()) {
       output.write(num._data, sizeof(num));
   }
   output.close();
   return 0;
}

edited Mar 14 '11 at 08:55

answered Feb 26 '11 at 16:05

Errata

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6
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1

You shouldn't name your members with preceding underscores. Names with preceding underscores are reserved for the compiler. See http://stackoverflow.com/questions/228783/what-are-the-rules-about-using-an-underscore-in-a-c-identifier. – Emile Cormier Feb 26 '11 at 16:52
1

@Emile: these ones aren't. Member names are not "in the global namespace". – Steve Jessop Feb 26 '11 at 16:59

GolezTrol · Accepted Answer · 2017-01-18T08:54:51.600

1

http://www.cplusplus.com/doc/tutorial/files/ It's good to read the whole thing, but the information you need is in 'Binary files' in the bottom half of the article.

ofstream outputFile;
outputFile.open("yourfile.dat");
unsigned short int i;
i = 10;
outputFile.write(&i, sizeof(i));

outputFile.close();

edited Jan 18 '17 at 08:54

answered Feb 26 '11 at 15:37

GolezTrol

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It doesn't work. `/mnt/Dane/Projects/Discoverer/Discoverer/src/MapClass/SaveMap.cpp|92|error: no matching function for call to ‘std::basic_fstream >::write(short unsigned int*, int)’|` – m4tx Feb 26 '11 at 15:49
4

Instead of `outputFile.write(&i, 2);` try `outputFile.write(reinterpret_cast(&i), sizeof(i));` – Emile Cormier Feb 26 '11 at 16:37
1

`sizeof(i)` or `sizeof(unsigned short)` would be preferrable to the hard-coded `2`. – Emile Cormier Feb 26 '11 at 16:46

score 1 · Answer 3 · answered Mar 14 '11 at 09:25

If you have to use stdio.h (and not iostream):

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

int main(void)
{
  FILE* f;
  unsigned short int i = 5;
  f=fopen("yourfile","w");
  if(f == NULL)
    {
      perror("yourfile is not open");
      exit(EXIT_FAILURE);
    }
  fwrite(&i,sizeof(i),1,f);
  fclose(f);
  return 0;
}

Short int - how to save to the file

3 Answers3