Segmentation fault on end of loop... (getline)

[jan247]

hi, im new here... um, this code works except that, at the end of the
loop, i always get a "Segmentation fault". Can anyone help me on this?

using GNU C:

.....
FILE *fp;
fp = fopen("./prg.c", "r");

char *line;
int x=1;
int nbytes = 100;
while(getline( &line, &nbytes, fp ) != -1)
{
printf("%d: %s", x, line );
x++;
}
fclose(fp);
.....

 

[August Karlstrom]

jan247 wrote:
-snip-

FILE *fp;
fp = fopen("./prg.c", "r");

char *line;
int x=1;
int nbytes = 100;
while(getline( &line, &nbytes, fp ) != -1)
{
printf("%d: %s", x, line );
x++;
}
fclose(fp);

-snip-

You have to allocate memory for `line' before you can use getline:

line = malloc(nbytes + 1);
...


August

 

[Keith Thompson]

hi, im new here... um, this code works except that, at the end of the
loop, i always get a "Segmentation fault". Can anyone help me on this?

using GNU C:

....
FILE *fp;
fp = fopen("./prg.c", "r");

char *line;
int x=1;
int nbytes = 100;
while(getline( &line, &nbytes, fp ) != -1)
{
printf("%d: %s", x, line );
x++;
}
fclose(fp);
....

You call fopen(), but you don't check whether it succeeded.

getline() is not a standard C function.

<OT>
You might look into what getline() does if its first argument is a
pointer to an uninitialized pointer object (the value of line is
garbage).

You might also look at the type of the second argument.
</OT>

 

[pemo]

hi, im new here... um, this code works except that, at the end of the
loop, i always get a "Segmentation fault". Can anyone help me on this?

using GNU C:

....
FILE *fp;
fp = fopen("./prg.c", "r");

char *line;
int x=1;
int nbytes = 100;
while(getline( &line, &nbytes, fp ) != -1)
{
printf("%d: %s", x, line );
x++;
}
fclose(fp);
....

See what the others have said, plus, use fgets instead of getline.

 

[Richard Heathfield]

pemo said:

See what the others have said, plus, use fgets instead of getline.

The two do not perform the same task. The getline function does a job which
no single standard library function can do. On the other hand, it isn't a
standard ISO C function. The decision about which to use is not as
clear-cut as you make it sound.

 

[Keith Thompson]

hi, im new here... um, this code works except that, at the end of the
loop, i always get a "Segmentation fault". Can anyone help me on this?

using GNU C:

.... [snip]
while(getline( &line, &nbytes, fp ) != -1)

[snip]

See what the others have said, plus, use fgets instead of getline.

fgets() is standard, while getline() is a GNU extension, so that's
good advice if you're concerned about portability. However, getline()
does have some advantages over fgets() (I won't go into the details),
so it's perfectly appropriate to use it if portability to non-GNU
implementations isn't a concern.

 

[M. Nejat AYDIN]

hi, im new here... um, this code works except that, at the end of the
loop, i always get a "Segmentation fault". Can anyone help me on this?

using GNU C:
FILE *fp;
fp = fopen("./prg.c", "r");

You must check the value of fp here.

char *line;
int x=1;
int nbytes = 100;
while(getline( &line, &nbytes, fp ) != -1)
{
printf("%d: %s", x, line );
x++;
}
fclose(fp);

getline is not a standard C function; it is a GNU extension,
but it is not too difficult to implement it in terms of standard
functions.

<OT>
You should set the line pointer to NULL, or a value returned from
a call to malloc, before the first call to getline. For example;
size_t nbytes = 0;
char *line = NULL;
or alternatively,
size_t nbytes = 100; /* any value should work */
char *line = malloc(nbytes);

Read manual page of getline for the details.
</OT>