NULL struct at end of declared array of structs

[JennyWren]

I have an array of structs which I will be going through one-by-one to search for a matching value. This array might have elements added and removed later, so I don't want to have to update a defined size for the array. What I'd like to do is put a NULL struct at the end so that the end can be detected.

Here's some code:

typedef struct smfMolTrans {
  char molecule[SZFITSCARD]; /* molecule species */
  char transiti[SZFITSCARD]; /* transition */
  double freq;               /* frequency of transition */
} molTrans;

static molTrans *transitions[] = {
{"SO", "4 5 - 3 4", 178605.403000},
{"CH", "2 -1 3 3 - 2 1 2 2", 178875.247400},
{"SiCC", "8 0 8 - 7 0 7", 179446.496000},
/*.... a bunch more....*/
};

Then later I want to be able to do something like

while ( transitions[i] != NULL ) {
/* check to see if the frequency matches, do some stuff... */
}

Basically I need to be able to know when to quit searching through the array. When I try putting a NULL at the end of the array:

static molTrans transitions[] = {
{"SO", "4 5 - 3 4", 178605.403000},
{"CH", "2 -1 3 3 - 2 1 2 2", 178875.247400},
{"SiCC", "8 0 8 - 7 0 7", 179446.496000},
/*.... a bunch more....*/
NULL
};

I get "warning: initialization makes integer from pointer without a cast" (for the initialization of the array) and "error: invalid operands to binary !=" (for the while loop).

Suggestions?

[Laharl]

One solution is to create a set of values (maybe "", "", and 0) and treat that as your NULL struct. Another is to use a linked list of structs rather than an array. You'd (probably) need another struct that has a moltrans as its data member, along with a pointer to the next node in the list.

[weaknessforcats]

This array might have elements added and removed later, so I don't want to have to update a defined size for the array.

By definition an array has a fixed size.

That means you have a variable for the number of elements. Use that variable to know when you are at the end of the array.

Only a char array with a NULL gets special treatment as a "string".

Are you using C++? You don't say, but if you are, the vector implements an elastic array that expands and contracts.

Also, instead of an array, could you use a double-linked list?