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I'm going through my program with valgrind to hunt down memory leaks. Here's one that I'm not sure what to do with.
==15634== 500 (224 direct, 276 indirect) bytes in 2 blocks are definitely lost in loss record 73 of 392 ==15634== at 0x4007070: realloc (vg_replace_malloc.c:429) ==15634== by 0x807D5C2: hash_set_column(HASH*, int, char const*) (Hash.cpp:243) ==15634== by 0x807BB15: LCD::PluginDiskstats::PluginDiskstats() (PluginDiskstats.cpp:102) ==15634== by 0x806E021: LCD::Evaluator::Evaluator() (Evaluator.cpp:27) ==15634== by 0x8066A87: LCD::LCDControl::LCDControl() (LCDControl.h:16) ==15634== by 0x80667F5: main (Main.cpp:8)
Here's the code:
/* add an entry to the column header table */
void hash_set_column(HASH * Hash, const int number, const char *column)
{
if (Hash == NULL)
return;
Hash->nColumns++;
Hash->Columns = (HASH_COLUMN *)realloc(Hash->Columns, Hash->nColumns * sizeof(HASH_COLUMN)); // line 243
Hash->Columns[Hash->nColumns - 1].key = strdup(column);
Hash->Columns[Hash->nColumns - 1].val = number;
qsort(Hash->Columns, Hash->nColumns, sizeof(HASH_COLUMN), hash_sort_column);
}
Should I be doing something here in regards to memory management?
541
In the C Programming Language, the realloc function is used to resize a block of memory that was previously allocated. The realloc function allocates a block of memory (which be can make it larger or smaller in size than the original) and copies the contents of the old block to the new block of memory, if necessary.
What is the difference between malloc() and calloc and realloc? The malloc() is used to allocate a single block of memory, calloc() is used to allocate multiple blocks of memory, and realloc()is used to reallocate memory that is allocated to malloc() or calloc() functions.
The function realloc is used to resize the memory block which is allocated by malloc or calloc before. Here is the syntax of realloc in C language, void *realloc(void *pointer, size_t size) Here, pointer − The pointer which is pointing the previously allocated memory block by malloc or calloc.
Once you call realloc() , you do not have to free() the memory addressed by pointer passed to realloc() - you have to free() the memory addressed by the pointer realloc() returns. (Unless realloc() returns NULL , in which case the original block of memory - passed to realloc() - has to be free() 'd.)
The problem is that if realloc() fails the function will return NULL but the original block will still be allocated. However, you've just overwritten the pointer to that block and can't free (or use) it anymore.
139
If realloc() fails it returns null and the original block is not freed. This line:
Hash->Columns = (HASH_COLUMN *)realloc(Hash->Columns, Hash->nColumns * sizeof(HASH_COLUMN)); // line 243
doesn't check the return value. So if realloc() fails null is written into Hash->Columns and the original block is leaked.
22
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