fwrite fails to write value 10 (0x0A)

Question

I was experimenting on creating BMP files from scratch, when I found a weird bug I could not explain. I isolated the bug in this minimalist program: ``` int main() { FILE* ptr=NULL; int success=0,pos=0; ptr=fopen("test.bin","w"); if (ptr==NULL) { return 1; } char c[3]={10,11,10}; success=fwrite(c,1,3,ptr); pos=ftell(ptr); printf("success=%d, pos=%d
",success,pos); return 0; } ``` the output is: ``` success=3, pos=5 ``` with hex dump of the `test.bin` file being: ``` 0D 0A 0B 0D 0A ``` In short, whatever value you put instead of `11` (0x0B), `fwrite` will write it correctly. But for some reason, when `fwrite` comes across a `10` (0x0A) - and precisely this value - it writes `0D 0A` instead, that is, 2 bytes, although I clearly specified 1 byte per write in the `fwrite` arguments. Thus the 3 bytes written, as can be seen in the `success` variable, and the mysterious `5` in the `ftell` result. Could someone please tell me what the heck is going on here...and why 10, why not 97 or 28?? T…

Accepted Answer

Your file was opened in text mode so CRLF translation is being done. Try:

```
fopen("test.bin","wb");
```

fwrite fails to write value 10 (0x0A)

Solution

Problem