GhostKid Yao GhostKid Yao -4 years ago 158
C Question

How do I properly free memory related to getline() function?

I just started programming and have a beginner question, I want to write a function to read a file with unknown length line by line. Since I wouldn't know the length of each line so I used

getline()
function:

void readDict(FILE *dict_file){
//Read dic
char *line;
size_t len = 0, read;
while((read = getline(&line, &len, dict_file))!=-1){
check(line);
}
free(line);
return;
}


Since
getline()
is kind of similar to
malloc()
and
realloc()
a string, so if I keep using this function to read a lot of line with unknown length, would I get a memory leak or out of memory?

Answer Source

First of all, you should initialize lineptr to NULL. Without a proper initialization, lineptr will contain indeterminate value, which makes lineptr to point to invalid memory location and later in process, it will invoke undefined behavior while trying to allocate (realloc()) appropriate amount of memory.

Then, as per the man page,

[...] before calling getline(), *lineptr can contain a pointer to a malloc()-allocated buffer *n bytes in size. If the buffer is not large enough to hold the line, getline() resizes it with realloc(), updating *lineptr and *n as necessary.

So, as long as you pass the same *lineptr, you should be OK if you free() only once in the end.

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