Possible Duplicate:
Learning C by K&R, error when trying to compile programs from book with arrays and function calls
While learning The C Programming Language by Brian W. Kernighan and Dennis M. Ritchie, I tried the example in section 1.9 Character Arrays. Here are the codes:
/* read a set of text lines and print the longest */
#include <stdio.h>
#define MAXLINE 1000 /* maximum input line length */
/* declare functions: getline() and copy() */
int getline(char line[], int maxline);
void copy(char to[], char from[]);
/* getline: read a line into array "s", return length */
int getline(char s[], int lim)
{
int c, i;
for (i=0; i < lim-1 && (c=getchar())!=EOF && c!='\n'; ++i)
s[i] = c;
if (c == "\n"){
s[i] = c;
++i;
}
s[i] = '\0'; /* the null character whose value is 0 */
return i;
}
/* copy: copy 'from' into 'to'; assume to is big enough */
/* the return type of copy is "void" -- no value is returned */
void copy(char to[], char from[])
{
int i;
i = 0;
while ((to[i] = from[i]) != '\0') /* terminated with a \0 */
++i;
}
/* print the longest input line */
int main()
{
int len; /* current line length */
int max; /* maximum length seen so far */
char line[MAXLINE]; /* current input line */
char longest[MAXLINE]; /* longest line saved here */
max = 0;
while ((len = getline(line, MAXLINE)) > 0)
if (len > max) {
max = len;
copy(longest, line);
}
if (max>0) /* there was a line */
printf("%s", longest);
return 0;
}
There are two main errors:
The complete error list is here:
/Users/C/Codes/Ritchie/array_char.c:8: error: conflicting types for ‘getline’
/usr/include/stdio.h:449: error: previous declaration of ‘getline’ was here
/Users/C/Codes/Ritchie/array_char.c:13: error: conflicting types for ‘getline’
/usr/include/stdio.h:449: error: previous declaration of ‘getline’ was here
/Users/C/Codes/Ritchie/array_char.c: In function ‘getline’:
/Users//C/Codes/Ritchie/array_char.c:17: warning: comparison between pointer and integer
/Users/C/Codes/Ritchie/array_char.c:17: warning: comparison with string literal results in unspecified behavior
I am not sure what went wrong, since it is exactly the same code from the book. Maybe the declaration of functions at the beginning:
int getline(char line[], int maxline);
void copy(char to[], char from[]);
is problematic? Thank you!
http://www.kernel.org/doc/man-pages/online/pages/man3/getline.3.html
getline already exists in stdio.h. That is why you are getting the error. Change the function name to something else like getline_my.
Also, you are comparing a character with a string in line 16. It should be
if(c == '\n')
NOT
if(c == "\n")
The problem is that there is likely a definition of getline
in stdio.h
. On my version of linux there is a getline function supplied by the C library (part of the POSIX standard I think). You can't have two functions with the same name in C, and this is your problem. Try renaming your version of getline
to my_getline
(both where you declare/define it and where you use it).
/usr/include/stdio.h:449: error: previous declaration of ‘getline’ was here
It's exactly as it says: getline
is declared in stdio.h
(because the standard library provides a function with that name). You cannot provide your own function with that name, because when you call getline
, the compiler wouldn't know which one to use.
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