I want to decalre on 2d array, but I want to put a vrailbe into the declartaion

#define MAX_SIZE 512
char* FWdir;
int main()
{
 getFwDIR(FWdir);  //--> put In FWdir path example: /opt/fw1
 char arr [][MAX_SIZE] = {
 FWdir,"-t","arg"
};

}

try to iterate over arr in ,didnt get the /opt/fw1 , instead I got an adress

I expoected to get

if I will print arr I waill get

/opt/fw1 -t arg... insead I get "someoutput" -t arg

CodePudding user response：

There are two problems here.

The first is you are passing the pointer FWdir to getFwDIR(), but FWdir is NULL, so getFwDIR() has nowhere to store the path. In its current formulation of getFwDIR(char *), that function cannot dynamically allocate memory for the path either.

The second is that you are attempting to write the contents of the string FWdir directly into the array arr, but that is not how strings work in C.

On the first point, you have two obvious options:

1. Rewrite getFwDIR() to accept a pointer to a pointer getFwDIR(char **), and dynamically allocate space for the path in that function:

int getFwDIR(char **p_path)
{
  ...
  *p_path = malloc(MAXIMUM_PATH_LENGTH   1);
  ... // Proceed to get the path
}

...
int main(void)
{
  getFwDIR(&FWdir);  //--> put In FWdir path example: /opt/fw1
...
}

But, this does leave the issue of freeing the memory later on.

2. Make FWdir a string with definite length, and pass that to getFwDIR():

#define MAX_SIZE 512
char FWdir[MAX_SIZE];

Since you have, in arr, effectively limited the path length to 511 characters anyway I would go for the second option, which is easier and safer.

On the second point, you also have two clear options:

1. Declare the 2d array first, and pass the first element to getFwDIR():

 char arr [][MAX_SIZE] =
 {
   "","-t","arg"
 };
 getFwDIR(arr[0]);  //--> put In FWdir path example: /opt/fw1

In this one, you do not need FWdir.

2. Copy FWdir into the array after initialisation:

 char FWdir[MAX_SIZE];
 getFwDIR(FWdir);  //--> put In FWdir path example: /opt/fw1
 char arr [][MAX_SIZE] =
 {
   "","-t","arg"
 };
 strncpy(arr[0], FWdir, sizeof(arr[0]));