Memory leak with function getline. (Still reachable)

Question

Here's my piece of code(the purpose is to read line and make a structure out of it):

typedef struct{
   size_t length;
   char *letters;
}line;

static line ReadLine(){
    char *buffor = NULL;
    size_t length = 0;
    int nRead = 0;
    nRead = getline(&buffor, &length, stdin);
    return nRead == -1 ? (line) {.length = 0, .letters = NULL} : (line) {.length = nRead, .letters = buffor};
}

Later on in my main function I free the buffor that was allocated by getline function:

void ReadFile(){
line l = ReadLine();
printLine(l);
free(l.letters);
}

And yet i get that there is some memory(using valgrind): Leak_StillReachable by malloc in which the function getline is.

How do you “get” that there is some memory that was not freed? Does some tool tell you that? What does it say? Show the exact output of that tool. Or do you deduce it from the behavior of your program. What behavior? Edit the question to provide a [mre]. — Eric Postpischil, May 17 '21 at 12:50
I used valgrind(edited initial post) and I get Leak_StillReachable in the same line in which function getline() is. — Yashiru99, May 17 '21 at 12:56
I've tested your code with valgrind : _"All heap blocks were freed -- no leaks are possible"_. Could you give your `printLine` function in case of ? — Zilog80, May 17 '21 at 13:09
It doesn't modify buffer in any way, just printing it using printf function. Though I am using Clion valgring, this might be a problem? — Yashiru99, May 17 '21 at 13:17
Then i guess it's a problem with your local libc `getline` implementation (see [this question as example](https://stackoverflow.com/questions/30499809/valgrind-memory-leak-reachable?rq=1)) — Zilog80, May 17 '21 at 13:42

score 1 · Answer 1 · answered May 23 '21 at 06:18

Okay, so after some time I figured out that if getline() fails to allocate memory it still allocates the buffer, so f.e if nRead == -1(which indicates an error in getline) we have to free the buffer. Otherwise I return

(line) {.length = 0, .letters = NULL}

And I lose a pointer to buffer, which was despite an error allocated.

score 0 · Answer 2 · answered May 17 '21 at 13:04

0

Memory for getline() should be allocated using malloc(), try to change line (char* buffor = NULL) with line (char* buffor = (char*)malloc(count * sizeof(char)); ) where count is the max length for input string.

answered May 17 '21 at 13:04

otokkk

21
3

2

getline() calls realloc itself if there is no enough space allocated, that may cause the issue you mentioned. – otokkk May 17 '21 at 13:05
_"If *lineptr is NULL, then getline() will allocate a buffer for storing the line, which should be freed by the user program. (In this case, the value in *n is ignored.)"_ (man getline) – Zilog80 May 17 '21 at 13:06
In case of `realloc`, the preceding allocated space is freed by `realloc` : _"f the new size of the memory object would require movement of the object, the space for the previous instantiation of the object is freed"_ – Zilog80 May 17 '21 at 13:13
There is no maximum input length specified. – Yashiru99 May 17 '21 at 13:16

Memory leak with function getline. (Still reachable)

2 Answers2