Cannot free fileName char * after fclose

Question

I am trying to free my file name (char * pointer) but got an error :

Heap corruption detected: after normal block (#65) at 0x....

The code:

static FILE *initializeIndexFile(char *database, char **indexFileName)
{
    FILE *file1_p;
    *indexFileName = NULL;
    int len = strlen(database);
    *indexFileName = (char *)malloc(len *sizeof(char) + 1);
    strcpy(*indexFileName, database);
    file1_p = fopen(strcat(*indexFileName, ".ind"), "rb");
    if (file1_p == NULL)
        Handle_Failure();
    fclose(file1_p);
    free(*indexFileName);
    return file1_p;
}

Firstly I tought it because the file is still open so I make fclose() calling but still its got the same error.

Standard Warning : Please [do not cast](http://stackoverflow.com/q/605845/2173917) the return value of `malloc()` and family in `C`. — Sourav Ghosh, Jun 12 '15 at 07:06
Just wanna add, according to your cde, you don't need to get a `char **`, a simple `char *` should be enough here. This may help you debugging some stuff too — Guillaume Munsch, Jun 12 '15 at 07:11
@LeZohan68 Unless he wants the indexFileName in caller function for some purpose. — Mohit Jain, Jun 12 '15 at 07:11
@MohitJain if i'm not wrong, it's already a pointer. The content should be modified. And he wants to malloc over, so ... — Guillaume Munsch, Jun 12 '15 at 07:14
@LeZohan68 Yes if he modifies the contents only. If you update a pointer (NULL, malloc etc), you are actually discarding the copy of that pointer and giving new value to your local pointer and the pointer in caller function remains same. — Mohit Jain, Jun 12 '15 at 07:15

score 2 · Accepted Answer · edited May 23 '17 at 11:51

2

You code is having issue in the below line

strcat(*indexFileName, ".ind")

the destination buffer at *indexFileName is having insufficient memory to hold the concatenated string. Hence it invokes undefined behaviour.

From the man page of strcat()

... If dest (destination buffer) is not large enough, program behaviour is unpredictable;

So, once it invokes UB, there is no particular behaviour you can predict or expect.

That said,

Please do not cast the return value of malloc() and family in C.
sizeof(char) is guranteed to be 1 by C standard. You son't need to use that.

Solution ^{[From the deleted answer by Mr. Mohit Jain]}

Revise your allocation to:

int len = strlen(database) + strlen(".ind");   //allocate enough space to hold
*indexFileName = (char *)malloc(len + 1);      // the final concatenated string

edited May 23 '17 at 11:51

Community

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answered Jun 12 '15 at 07:07

Sourav Ghosh

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This covers almost everything. – Mohit Jain Jun 12 '15 at 07:14
@MohitJain Thanks sir. Why did you delete your answer? Just now I saw it, it is a good answer. I'm going to _blatantly_ copy the solution part from your answer, with your permission. :-) – Sourav Ghosh Jun 12 '15 at 07:17
1

Sure please go ahead. There is no point of 2 similar answers. – Mohit Jain Jun 12 '15 at 07:18
@MohitJain Done. Now it looks complete. :-) – Sourav Ghosh Jun 12 '15 at 07:21

LPs · Answer 2 · 2015-06-12T07:11:36.403

0

This

*indexFileName = (char *)malloc( len *sizeof(char) + 1);

must be

*indexFileName = (char *)malloc( len *sizeof(char) + 5);

due to the extention adding with

strcat(*indexFileName, ".ind")

edited Jun 12 '15 at 07:11

answered Jun 12 '15 at 07:09

LPs

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score 0 · Answer 3 · answered Jun 12 '15 at 07:14

0

I suppose the problem is in "strcpy(*indexFileName, database);" instruction,

it should be strcpy(indexFileName, database);

answered Jun 12 '15 at 07:14

Chirag Gangdev

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Cannot free fileName char * after fclose

3 Answers3