CODEWITHSUNDEEP
cfwriteprintf
Shai Balassiano
Shai Balassiano

Reputation: 1007

how to write an integer to a file (the difference between fprintf and fwrite)

I've been trying to write an integer to a file (open mode is w). fprintf wrote it correctly but fwrite wrote gibberish:

int length;
char * word = "word";

counter = strlen(word);
fwrite(&length, sizeof(int), 1, file);
fwrite(word, sizeof(char), length, file);

and the result in the file is:

word

but if I use fprintf instead, like this:

int length;
char * word = "word";

counter = strlen(firstWord);
fprintf(file, "%d", counter);
fwrite(word, sizeof(char), length, file);

I get this result in the file:

4word

can anyone tell what I did wrong? thanks!

update: I would eventually like to change the writing to binary (I will open the file in wb mode), will there be a difference in my implementation?

Upvotes: 15

Views: 47398

Answers (2)

David R Tribble
David R Tribble

Reputation: 12204

Using printf() converts the integer into a series of characters, in this case "4". Using fwrite() causes the actual bytes comprising the integer value to be written, in this case, the 4 bytes for the characters 'w', 'o', 'r', and 'd'.

Upvotes: 1

vanza
vanza

Reputation: 9903

fprintf writes a string. fwrite writes bytes. So in your first case, you're writing the bytes that represent an integer to the file; if its value is "4", the four bytes will be in the non-printable ASCII range, so you won't see them in a text editor. But if you look at the size of the file, it will probably be 8, not 4 bytes.

Upvotes: 23

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