printf(string) vs. printf("%s", string)

Question

I'm writing a proxy server, and I ran into a curious bug that I hoped someone would be able to explain. I'm receiving the first line of a GET request from client. For example, the client would send the request: ``` GET http://en.wikipedia.org/wiki/Special:Random HTTP/1.0 Host: en.wikipedia.org ... ``` And I would forward this request to the server. However, with certain web addresses, I would encounter a problem: ``` GET http://map.media6degrees.com/orbserv/curl=http%3A%2F%2Fwww.masteringemacs.org%2Farticles[trunc] HTTP/1.0 ``` I read this line into `char buffer[MAXLINE_LENGTH]`, which is long enough to hold the string. When I print the received get request with ``` printf(buffer); ``` The printed string is: ``` GET http://map.media6degrees.com/orbserv/hbpix?pixId=2869&curl=http0X0.0000000000015P-10220.0000000.000000www.masteringemacs.org0.000000articles0.00000020100.000000110.000000010.000000running-shells-in-emacs-overview2047419954308499624822282711545024564232847339561180412063158…

Accepted Answer

1) If you look at the function prototype, you'll see that printf() expects a format string, and zero or more arguments. So, strictly speaking, "printf(string)" is not correct:

```
SYNOPSIS
       #include <stdio.h>

int printf(const char *format, ...);
       int fprintf(FILE *stream, const char *format, ...);
       int sprintf(char *str, const char *format, ...);
       int snprintf(char *str, size_t size, const  char  *format,
       ...);
```

2) The first argument will be interpreted as a format string, and any "%XXX" entries it found will be interpreted as place holders. Which it sounds like is exactly what's happening :)

3) The solution, of course, is `printf ("%s", string)`

4) Or using `puts(string)` instead :)

printf(string) vs. printf("%s", string)

Solution

Problem