Ct_param illegal value of 0

I'm using sybase 15/12.5 with CS_VERSION_100

When i try to use the ct_param i get an error:

An illegal value of 0 was placed in the status field of the CS_DATAFMT structure.

But, i create my structure with.

CS_DATAFMT datafmt;
strcpy(datafmt.name, "@interface");
datafmt.namelen = 11;
datafmt.datatype=CS_INT_TYPE;
datafmt.maxlength=4;
datafmt.status=CS_INPUTVALUE;
datafmt.locale = NULL;
datafmt.format = 0;
datafmt.scale = -99999;
datafmt.count = 1;
datafmt.usertype=0;

ct_param(command, &datafmt, /* value 300 */, 4, 0)

When i do it with a varchar it returns 1 (true), but of course it tells to me that i'm trying to put a varchar param in a place of a int param.