I have a char array in typedef struct, which is too big (around 260k)
#define LENGTH 260000
typedef struct {
int longSize;
char hello[LENGTH ];
} p_msg;
I would like to use malloc on this char array which as below:
typedef struct {
int longSize;
char * hello= malloc(sizeof(char));
} p_msg;
But it gave me error:
error: expected ':', ',', ';', '}' or '__attribute__' before '=' token
How can I malloc the char array?
You can't call a function from within a struct definition. You should instead simply keep your first struct definition with the large string inside, and then do malloc(sizeof(p_msg)) when you want to create one.
Or you can keep it with the pointer inside, and remember to initialize that pointer with the result of malloc() every time you create a struct instance.
If you have a function taking the struct by pointer, you can do this:
int extMsg(p_msg *msgBuffer)
{
msgBuffer->longSize = 12;
msgBuffer->hello = malloc(12);
snprintf(msgBuffer->hello, 12, "hello %d", 42);
return 0;
}
You need to use pointer types, consider this code:
#include <stdlib.h>
#include <string.h>
typedef struct {
int longSize;
char * hello;
} p_msg;
int main()
{
p_msg msg;
//zeroing memory to set the initial values
memset(&msg, 0, sizeof(p_msg));
//storing the size of char array
msg.longSize = 260000;
//dynamically allocating array using stored value
msg.hello = (char *)malloc(msg.longSize);
//using msg struct in some function
int retVal = someFunc(&msg);
//free hello array after you don't need it
free(msg.hello);
msg.hello = 0;
}
malloc(LENGTH)instead ofmalloc(sizeof(char))(forLENGTHchars,sizeof(char)is always 1), though you can't do it in the type definition like that.