I am trying to use getline
and a char pointer to store all results of getline
to that one pointer:
char *final = NULL;
char *line = NULL;
size_t n = 0;
ssize_t result;
int current_size = 0;
while ((result = getline(&line, &n, in)) != -1){
current_size += result;
final = realloc(final, current_size ); //valgrind error
if (final== NULL)
return NULL;
strcat(final,line);
}
But I always get the error:
==695== Conditional jump or move depends on uninitialised value(s)
==695== at 0x483B6D0: malloc (in /usr/lib/x86_64-linux-gnu/valgrind/vgpreload_memcheck-amd64-linux.so)
==695== by 0x483E017: realloc (in /usr/lib/x86_64-linux-gnu/valgrind/vgpreload_memcheck-amd64-linux.so)
... method trace
I know, that realloc just allocates, not initalises values, but if I try to memset in the next line, valgrind tells me:
==695== Conditional jump or move depends on uninitialised value(s)
==695== at 0x48428EC: memset (in /usr/lib/x86_64-linux-gnu/valgrind/vgpreload_memcheck-amd64-linux.so)
... method trace
I read a lot of SO contributions, but could not manage to fix that problem with the solutions shown in those. I am sure that that's not the worst memory-leak, but it's still one, so I am trying to fix it. Has anyone an idea how to fix that?
You are close, but your use of current_size += result;
before the call to realloc()
prevents a simple check of current_size == 0
to check for the first iteration which you would then want to initialize final
as an empty-string.
You can do the following:
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
int main (void) {
char *final = NULL, *line = NULL;
size_t n = 0, current_size = 0;
ssize_t result;
while ((result = getline(&line, &n, stdin)) != -1) {
if (result > 0)
line[--result] = 0; /* trim \n */
final = realloc (final, current_size + result + 1); /* add room for \0 */
if (final== NULL) /* validate allocation */
return 1;
if (!current_size) /* if 1st word */
*final = 0; /* make final empty-str */
current_size += result; /* now update value */
strcat (final, line); /* concatenate */
}
printf ("%zu - %s\n", current_size, final);
free (final);
free (line);
}
Example Use/Output
$ ./bin/getlineplusone << 'eof'
1234
56
789
eof
9 - 123456789
Memory Use/Error Check
$ valgrind ./bin/getlineplusone << 'eof'
1234
56
789
eof
==8438== Memcheck, a memory error detector
==8438== Copyright (C) 2002-2017, and GNU GPL'd, by Julian Seward et al.
==8438== Using Valgrind-3.13.0 and LibVEX; rerun with -h for copyright info
==8438== Command: ./bin/getlineplusone
==8438==
9 - 123456789
==8438==
==8438== HEAP SUMMARY:
==8438== in use at exit: 0 bytes in 0 blocks
==8438== total heap usage: 6 allocs, 6 frees, 5,262 bytes allocated
==8438==
==8438== All heap blocks were freed -- no leaks are possible
==8438==
==8438== For counts of detected and suppressed errors, rerun with: -v
==8438== ERROR SUMMARY: 0 errors from 0 contexts (suppressed: 0 from 0)