---
name: "sdrlist"
section: "3"
platform: "linux"
package: "ion-doc"
version: "3.2.1+dfsg-1.1"
release: "Debian 9 (Stretch)"
platforms: ["linux"]
url: "https://new.carta.tech/sdrlist"
---

# sdrlist(3)

Simple Data Recorder list management functions

## NAME

sdrlist - Simple Data Recorder list management functions

## SYNOPSIS

```
    #include "sdr.h"
    typedef int (*SdrListCompareFn)(Sdr sdr, Address eltData, void *argData);
    typedef void (*SdrListDeleteFn)(Sdr sdr, Object elt, void *argument);
    [see description for available functions]
```

## DESCRIPTION

The SDR list management functions manage doubly-linked lists in managed SDR heap space.  The functions manage two kinds of objects: lists and list elements.  A list knows how many elements it contains and what its start and end elements are.  An element knows what list it belongs to and the elements before and after it in the list.  An element also knows its content, which is normally the SDR Address of some object in the SDR heap.  A list may be sorted, which speeds the process of searching for a particular element.

- Object sdr\_list\_create(Sdr sdr)

  Creates a new list object in the SDR; the new list object initially  contains no list elements.  Returns the address of the new list, or  zero on any error.

- void sdr\_list\_destroy(Sdr sdr, Object list, SdrListDeleteFn fn, void \*arg)

  Destroys a list, freeing all elements of list.  If *fn* is non-NULL, that function is called once for each freed element; when called, *fn* is passed the Address that is the element's data and the *argument* pointer passed to *sdr\_list\_destroy()*.

  Do not use *sdr\_free* to destroy an SDR list, as this would leave the elements of the list allocated yet unreferenced.

- int sdr\_list\_length(Sdr sdr, Object list)

  Returns the number of elements in the list, or -1 on any error.

- void sdr\_list\_user\_data\_set(Sdr sdr, Object list, Address userData)

  Sets the "user data" word of *list* to *userData*.  Note that *userData* is nominally an Address but can in fact be any value that occupies a single word.  It is typically used to point to an SDR object that somehow characterizes the list as a whole, such as a name.

- Address sdr\_list\_user\_data(Sdr sdr, Object list)

  Returns the value of the "user data" word of *list*, or zero on any error.

- Object sdr\_list\_insert(Sdr sdr, Object list, Address data, SdrListCompareFn fn, void \*dataBuffer)

  Creates a new list element whose data value is *data* and inserts that element into the list.  If *fn* is NULL, the new list element is simply appended to the list; otherwise, the new list element is inserted after the last element in the list whose data value is "less than or equal to" the data value of the new element (in dataBuffer) according to the collating sequence established by *fn*.  Returns the address of the newly created element, or zero on any error.

- Object sdr\_list\_insert\_first(Sdr sdr, Object list, Address data)

  - Object sdr\_list\_insert\_last(Sdr sdr, Object list, Address data)

  Creates a new element and inserts it at the front/end of the list.  This function should not be used to insert a new  element into any ordered list; use *sdr\_list\_insert()* instead.   Returns the address of the newly created list element on success, or zero on any error.

- Object sdr\_list\_insert\_before(Sdr sdr, Object elt, Address data)

  - Object sdr\_list\_insert\_after(Sdr sdr, Object elt, Address data)

  Creates a new element and inserts it before/after the specified list element.  This function should not be used to insert a new element into any ordered list; use *sdr\_list\_insert()* instead.  Returns the address of the newly  created list element, or zero on any error.

- void sdr\_list\_delete(Sdr sdr, Object elt, SdrListDeleteFn fn, void \*arg)

  Delete *elt* from the list it is in. If *fn* is non-NULL, that function will be called upon deletion of *elt*; when called, that function is passed the Address that is the list element's data value and the *arg* pointer passed to *sdr\_list\_delete()*.

- Object sdr\_list\_first(Sdr sdr, Object list)

  - Object sdr\_list\_last(Sdr sdr, Object list)

  Returns the address of the first/last element of *list*, or zero on any error.

- Object sdr\_list\_next(Sdr sdr, Object elt)

  - Object sdr\_list\_prev(Sdr sdr, Object elt)

  Returns the address of the element following/preceding *elt* in that element's list, or zero on any error.

- Object sdr\_list\_search(Sdr sdr, Object elt, int reverse, SdrListCompareFn fn, void \*dataBuffer);

  Search a list for an element whose data matches the data in *dataBuffer*, starting at the indicated initial list element.  If the *compare* function is non-NULL, the list is assumed to be sorted in the order implied by that function and the function is automatically called once for each element of the list until it returns a value that is greater than or equal to zero (where zero indicates an exact match and a value greater than zero indicates that the list contains no matching element); each time *compare* is called it is passed the Address that is the element's data value and the *dataBuffer* value passed to *sm\_list\_search()*. If *reverse* is non-zero, then the list is searched in reverse order (starting at the indicated initial list element) and the search ends when *compare* returns a value that is less than or equal to zero.  If *compare* is NULL, then the entire list is searched (in either forward or reverse order, as directed) until an element is located whose data value is equal to ((Address) *dataBuffer*).  Returns the address of the matching element if one is found, 0 otherwise.

- Object sdr\_list\_list(Sdr sdr, Object elt)

  Returns the address of the list to which *elt* belongs, or 0 on any error.

- Address sdr\_list\_data(Sdr sdr, Object elt)

  Returns the Address that is the data value of *elt*, or 0 on any error.

- Address sdr\_list\_data\_set(Sdr sdr, Object elt, Address data)

  Sets the data value for *elt* to *data*, replacing the original value.  Returns the original data value for *elt*, or 0 on any error.  The original data value for *elt* may or may not have been the address of an object in heap data space; even if it was, that object was NOT deleted.

  Warning: changing the data value of an element of an ordered list may ruin the ordering of the list.

## USAGE

When inserting elements or searching a list, the user may optionally provide a compare function of the form:

```
    int user_comp_name(Sdr sdr, Address eltData, void *dataBuffer);
```

When provided, this function is automatically called by the sdrlist function being invoked; when the function is called it is passed the content of a list element (*eltData*, nominally the Address of an item in the SDR's heap space) and an argument, *dataBuffer*, which is nominally the address in local memory of some other item in the same format. The user-supplied function normally compares some key values of the two data items and returns 0 if they are equal, an integer less than 0 if *eltData*'s key value is less than that of *dataBuffer*, and an integer greater than 0 if *eltData*'s key value is greater than that of *dataBuffer*.  These return values will produce a list in ascending order.   If the user desires the list to be in descending order, the function must reverse the signs of these return values.

When deleting an element or destroying a list, the user may optionally provide a delete function of the form:

```
    void user_delete_name(Sdr sdr, Address eltData, void *argData)
```

When provided, this function is automatically called by the sdrlist function being invoked; when the function is called it is passed the content of a list element (*eltData*, nominally the Address of an item in the SDR's heap space) and an argument, *argData*, which if non-NULL is normally the address in local memory of a data item providing context for the list element deletion. The user-supplied function performs any application-specific cleanup associated with deleting the element, such as freeing the element's content data item and/or other SDR heap space associated with the element.

## SEE ALSO

[*lyst*(3)](/lyst/3.md), [*sdr*(3)](/sdr/3.md), [*sdrstring*(3)](/sdrstring/3.md), [*sdrtable*(3)](/sdrtable/3.md), [*smlist*(3)](/smlist/3.md)