Allocating memory for struct within a struct in cycle

Question

I'm working on INI-style configuration parser for some project, and I gets next trouble. I have 3 structures:

typedef struct {
    const char* name;
    unsigned tract;
    int channel;
    const char* imitation_type;
} module_config;

typedef struct {
    int channel_number;
    int isWorking;
    int frequency;
    int moduleCount;
} channel_config;

typedef struct {
    int mode;
    module_config* module;
    channel_config* channel;
} settings; 

And I have function for handling data in my INI-file (I working under inih parser): [pasted to pastebin cause too long]. Finally, in main(), I did the next:

settings* main_settings;
main_settings = (settings*)malloc(sizeof(settings));
main_settings->module = (module_config*)malloc(sizeof(module_config));
main_settings->channel = (channel_config*)malloc(sizeof(channel_config));
if (ini_parse("test.ini", handler, &main_settings) < 0) {
    printf("Can't load 'test.ini'\n");
    return 1;
}

In result, binary crashes with memory fault. I think (no, I KNOW), what I'm incorrectly allocating the memory in handler(), but I does not understand, where I do it wrong. I spent all night long trying to understand memory allocating, and I'm very tired, but now me simply interestingly, what I'm doing wrong, and HOW to force this working fine. PS Sorry for ugly english

Answer 1

The problem seems to be related to the reallocation of your structs:

pconfig = (settings *) realloc(pconfig, (module_count + channel_count) * sizeof(channel_config));
pconfig->module = (module_config *) realloc(pconfig->module, module_count * sizeof(module_config));
pconfig->channel = (channel_config *) realloc(pconfig->channel, channel_count * sizeof(channel_config));

First of all, you must not reallocate the main settings struct. Since your handler will always be called with the original pconfig value, the reallocation of the module and channel arrays has no effect, and you'll access freed memory.

Also when reallocating the module and channel arrays you should allocate count + 1 elements, since the next invocation of handler might assign to the [count] slot.

So try to replace the three lines above with:

pconfig->module  = (module_config *)  realloc(pconfig->module,  (module_count + 1)  * sizeof(module_config));
pconfig->channel = (channel_config *) realloc(pconfig->channel, (channel_count + 1) * sizeof(channel_config));