# slow5_hdr_add

## NAME

slow5_hdr_add -  adds a new header data attribute to a SLOW5 header

## SYNOPSYS

`int slow5_hdr_add(const char *attr, slow5_hdr_t *header);`

## DESCRIPTION
`slow5_hdr_add()` add a new attribute name *attr* to a SLOW5 file header pointed by *header*.

The argument *header* points to a SLOW5 header of type *slow5_hdr_t* and typically this is the *s5p->header* member inside the *slow5_file_t \*s5p* returned by  `slow5_open()`.

## RETURN VALUE
Upon successful completion, `slow5_hdr_add()` returns a non negative integer (>=0). Otherwise, a negative value is returned that indicates the error.

## ERRORS

A negative returned when an error occurs and can be due to following occasions (not an exhaustive list):

- if an input argument is NULL
- if the attribute already exists
- if internal error

## NOTES


In the future `slow5_errno` will be set to indicate the error.

## EXAMPLES

```
#include <stdio.h>
#include <stdlib.h>
#include <slow5/slow5.h>

#define FILE_PATH "test.slow5"

int main(){

    slow5_file_t *sp = slow5_open(FILE_PATH, "w");
    if(sp==NULL){
        fprintf(stderr,"Error opening file!\n");
        exit(EXIT_FAILURE);
    }
    slow5_hdr_t* header = sp->header;

    //add a header group attribute called run_id
    if (slow5_hdr_add("run_id", header) < 0){
        fprintf(stderr,"Error adding run_id attribute\n");
        exit(EXIT_FAILURE);
    }
    //add another header group attribute called asic_id
    if (slow5_hdr_add("asic_id", header) < 0){
        fprintf(stderr,"Error adding asic_id attribute\n");
        exit(EXIT_FAILURE);
    }

    //....

}
```
