# slow5_get

## NAME

slow5_get - fetches a record from a SLOW5 file corresponding to a given read ID

## SYNOPSYS

`int slow5_get(const char *read_id, slow5_rec_t **read, slow5_file_t *s5p)`

## DESCRIPTION

`slow5_get()` fetches a record from a SLOW5 file *s5p* for a specified *read_id* into a *slow5_rec_t* and stores the address of the *slow5_rec_t* in **read*.

The argument  *read_id* points to a read identifier string.

If **read* is set to NULL before the call, then `slow5_get()` will allocate a *slow5_rec_t* for storing the record.
This *slow5_rec_t* should be freed by the user program using `slow5_rec_free()`.
Alternatively, before calling `slow5_get()`, **read* can contain a pointer to an allocated *slow5_rec_t* from a previous `slow5_get()` call.
If the allocated *slow5_rec_t* is not large enough to hold the record, `slow5_get()` will resize it internally.

The argument *s5p* points to a *slow5_file_t* opened using `slow5_open()`. `slow5_get()` requires the SLOW index to be pre-loaded to *s5p* using `slow5_idx_load()`.

`slow5_get()` does not affect the file pointer used by `slow5_get_next()`. `slow5_get()` can be called by multiple threads in parallel on the same *slow5_file_t* pointer.

## RETURN VALUE

Upon successful completion, `slow5_get()` returns a non negative integer (>=0). Otherwise, a negative value is returned that indicates the error and `slow5_errno` is set to indicate the error.

## ERRORS

* `SLOW5_ERR_NOTFOUND`  
         Read_id was not found in the index.
* `SLOW5_ERR_ARG`       
         Invalid argument - read_id, read or s5p is NULL.
* `SLOW5_ERR_RECPARSE`  
         Record parsing error.
* `SLOW5_ERR_NOIDX`     
         The index has not been loaded.
* `SLOW5_ERR_IO`        
         I/O error when reading the slow5 file, for instance, `pread()`failed.
* `SLOW5_ERR_MEM`        
         Memory allocation error.
* `SLOW5_ERR_UNK`        
         Slow5 file format is unknown.
* `SLOW5_ERR_PRESS`      
         Decompression error.

## NOTES

`slow5_get()` internally uses `pread()`.

## EXAMPLES

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

#define FILE_PATH "examples/example.slow5"

#define TO_PICOAMPS(RAW_VAL,DIGITISATION,OFFSET,RANGE) (((RAW_VAL)+(OFFSET))*((RANGE)/(DIGITISATION)))

int main(){

    slow5_file_t *sp = slow5_open(FILE_PATH,"r");
    if(sp==NULL){
       fprintf(stderr,"Error in opening file\n");
       exit(EXIT_FAILURE);
    }
    slow5_rec_t *rec = NULL;
    int ret=0;

    ret = slow5_idx_load(sp);
    if(ret<0){
        fprintf(stderr,"Error in loading index\n");
        exit(EXIT_FAILURE);
    }

    ret = slow5_get("r3", &rec, sp);
    if(ret < 0){
        fprintf(stderr,"Error when fetching the read\n");
    }
    else{
        printf("%s\t",rec->read_id);
        uint64_t len_raw_signal = rec->len_raw_signal;
        for(uint64_t i=0;i<len_raw_signal;i++){
            double pA = TO_PICOAMPS(rec->raw_signal[i],rec->digitisation,rec->offset,rec->range);
            printf("%f ",pA);
        }
        printf("\n");
    }

    slow5_rec_free(rec);

    slow5_idx_unload(sp);

    slow5_close(sp);

}
```

## SEE ALSO
[slow5_get_next()](slow5_get_next.md)