Interoperating with isCOBOL : isCOBOL and C : Calling C Language Functions and Other External Routines : COBOL and C Data Types
COBOL and C Data Types
As in other COBOL implementations, in order to successfully call C language functions from isCOBOL and exchange data, the C and COBOL data storage types must be matched.
For example:
In COBOL, an integer defined as
would be represented in C, as
77  MY-DATA-INT  SIGNED-INT    EXTERNAL
int  my_data_int;
When mapping C data types to COBOL, you can use COMP-5 or COMP-N as shown below.
C
COBOL
Data size
char[n], str[n], tchar[n]
PIC X(n)
n bytes
long, int
PIC X(4) COMP-N
or
PIC S9(9) COMP-5
4 bytes
dword, ulong, lpxxx, float
PIC X(4) COMP-N
or
PIC 9(9) COMP-5
4 bytes
short
PIC X(2) COMP-N
or
PIC S9(5) COMP-5
2 bytes
word, ushort
PIC X(2) COMP-N
or
PIC 9(5) COMP-5
2 bytes
Using COMP-N instead of COMP-5 is recommended for most cases.
C structures can be mapped to COBOL group items as follows:
C Structure
Equivalent COBOL group item
struct PERSON {
    int age;
    long ss;
    float weight;
    char name[25];
} family_member;
       01 PERSON.
          03 age    PIC X(4) COMP-N.
          03 ss     PIC X(4) COMP-N.
          03 weight PIC X(4) COMP-N.
          03 name   PIC X(25).