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# 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)
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