When I run my program , it calls a function that have a "char *msgtype" and this function work probably but when another function use a different "char *msgtype" in it when program reach the line that contain it , program crashes(and even when the firs function is called for second time program crashes). What is the problem ?
and if I change the name in the second function it just work one time and after calling that function again program crashes !
void fun1(){
...
cJSON *root = cJSON_Parse(buffer);
char *msgtype = cJSON_GetObjectItem(root,"type")->valuestring;
...
free(msgtype);
cJSON_Delete(root);
...
}
void fun2(){
...
cJSON *root = cJSON_Parse(buffer);
char *msgtype = cJSON_GetObjectItem(root,"type")->valuestring;//it crashes here
...
free(msgtype);
cJSON_Delete(root);
...
}
int main(){
fun1();
fun2();//it crashes inside this function !
}
Do you know what cJSON_GetObjectItem() returns? Is it a pointer into a data structure, or a copy of the data? If it returns a pointer to part of the bigger structure, that should not be freed with free() — it would be freed when you destroy the cjSON object.
If you take a look at the code for get_object_item() — which is called directly from cJSON_GetObjectItem() in cJSON.c, you will see it returns a pointer into the middle of a cJSON object. You cannot afford to call free() on that return value. You should only call cJSON_Delete() on the complete object. By calling free(msgtype), you are wrecking the integrity of the root data structure — and you probably end up with a double-free problem too.
If it is available for your platform, use Valgrind to analyze what's going wrong — it will probably tell you. If your system's malloc() implementation has debugging hooks (the version on macOS, for example, does), consider using them.