I need to write unsigned long long integer values to a text file. When I used fprintf() it works perfectly but, takes time. I have profiled my application and fprintf() takes the half of all time. I have made a research and I saw that, fwrite() is more effective than fprintf(). But I couldn't managed how to use it?
My code with fprintf()
fprintf(out, "%llu %llu\n", min, minv);
My code with fwrite()
fwrite(&min,sizeof(unsigned long long int),1, out);
fputs(" ",out);
fwrite(&minv,sizeof(unsigned long long int),1, out);
fputs("\n", out);
fwrite() is faster the first one but when I opened the file, the data is like
¾²ö `à ÔàUü
ؾ{4- "¤#sÏ$P
oD/
-5X®Z
How could I perform fwrite() properly in this situation?
... need to write unsigned long long integer values to a text file ...
The typical method to write an unsigned long long is the below. Note that the file is open in text mode.
out = fopen("data.out","w");
fprintf(out, " %llu", x);
To write faster, consider writing the text file file in binary mode. This will lose end-of-line translation, but may increase performance.
out = fopen("data.out","wb");
fprintf(out, " %llu", x);
If the compiler is weak, converting the unsigned long long to a string may further improve. A non-standard conversion function is needed. Some ideas here
out = fopen("data.out","wb");
char buf[50];
buf[0] = ' ';
size_t size = my_ulltoa(&buf[1], x); // returns size of the array used.
fwrite(buf, 1, 1 + size, 1, out);
OP's use of the below failed as it wrote a binary (e.g. 4 or 8 byte) representation to the text file, which is not readable as characters.
out = fopen("data.out","w");
// fails
fwrite(&min,sizeof(unsigned long long int),1, out);
Far faster is to write the binary representation to a binary file - but that is not readable as text.
// Works for non-text files
out = fopen("data.out","wb");
fwrite(&min, sizeof min, 1, out);