14

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?

Nicolas Kaiser
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Shai Balassiano
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2 Answers2

23

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.

vanza
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    so if I want to write an integer in a binary mode I should use fwrite, but if I write to the file textually I should use fprintf? – Shai Balassiano Jul 01 '11 at 20:46
1

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'.

David R Tribble
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