Reallocating a string that is passed in as a parameter - c

Question

I want to dynamically allocate only a portion of a character array.
So part of an array of size 100 is concrete. Say 10 is permanent memory, the other 90 is dynamic memory.
I made some attempt to read character by character until I decided to give up and take a shortcut idea I thought would work. However I end up getting an error that is
incorrect checksum for freed object - object was probably modified
after being freed
I use this method in a while loop in main and I pretty much free everything after the while loop processes. Because, I have the declaration outside of the while loop. I wanted to read an object in a while loop session since these objects end up being added into a list of objects. However the scope of the while loop causes segmentation problems, it cannot remember anything about the object. (I digress).
Here is my attempt.
Object* read(char* str)
{
Object* object = (Object*)malloc(sizeof(*object));
object->identity[0] = 0;
int capacity = (100 + 1) - (10);
object->name = (char*)malloc(capacity * sizeof(*object->name));
object->value = 0.0;
int length = strlen(str);
if (length > capacity)
object->name = (char*)realloc(object->name, (capacity * 2) * sizeof(*object->name));
int arguments = sscanf(str, "%" STRING_SPACE "s %lf %[^\n]s",
object->identity,
&object->value,
object->name);
if (arguments == MATCHER) {
return object;
} else {
return NULL;
}
return object;
}
In this case, an object has a variable sized name but a fixed amount of space allocated for its identity.
I tried something else with sscanf but realized it will never work because I read the string too late to assign memory to name. See;
/*
int len = 0;
for (char* itemObserve = item->name; *itemObserve; itemObserve++) {
if (len == sizeof(item->name)) {
capacity *= MULTIPLIER;
item->name = (char*)realloc(item->name, capacity * sizeof(*item->name));
}
len++;
}
*/
Here is the code in main, everything undefined is probably irrelevant to the bug:
int main()
{
FILE* stream;
Object* object;
ObjectList* list = initList();
while (true) {
char* line;
char cmd[15] = {0};
char* arg;
char* rest;
printf("> ");
line = getline(stdin);
arg = (char*)malloc(35 * sizeof(*arg));
rest = (char*)malloc(35 * sizeof(*rest));
int arguments = sscanf(line, "%s %s %[^\n]", cmd, arg, rest);
free(line);
line = NULL;
printf("\n");
if (strcmp(cmd, "add") == 0) {
arg = (char*)realloc(arg, (35 * 2) * sizeof(*arg));
sprintf(arg, "%s %s", arg, rest);
if ((object = read(arg)) == NULL) {
continue;
}
objectListAdd(list, object);
} else {
free(rest);
free(arg);
exit(EXIT_SUCCESS);
}
free(rest);
free(arg);
}
freeObject(object);
freeObjectList(list);
return EXIT_SUCCESS;
}
Separate getline function in main file
char* getline(FILE* stream)
{
int capacity = LINE_MAX + 1;
char* buffer = (char*)malloc(capacity * sizeof(*buffer));
int len = 0;
int ch;
while ((ch = fgetc(stream)) != '\n' && (ch != EOF)) {
if (len == capacity) {
capacity *= MULTIPLIER;
buffer = (char*)realloc(buffer, capacity * sizeof(*buffer));
}
buffer[len++] = ch;
}
if (ch == EOF) {
return NULL;
}
buffer[len] = '\0';
if (buffer == NULL)
return NULL;
return buffer;
}
There are other conditionals which work as a kind of command switch but they are irrelevant to the errors my program is exhibiting. This much I have narrowed the problem down to.