我编写了这个程序,它应该从用户输入创建一个整数链表,直到用户插入“0”,打印它,在它的末尾添加一个元素,然后再次打印链表,包括添加的元素。
运行时,输入和第一个输出工作正常,但在添加新元素时,我会收到以下错误消息:
“Project InsertElement在中引发了异常类‘External:SIGSEGV’”
文件“InsertElement”。第66行的lpr:输出端^。下一步:=RefNew;"
显然,第66行存在问题:
OutRefEnd^.next := RefNew;
但是我不知道这个问题是什么,如果它与我的代码有关,或者只是编译器的问题。据我所知,错误代码暗示“outRefEnd^”。next‘’指向一个空地址,但由于我给它赋值‘RefNew’,我不太明白为什么这首先会成为一个问题。
谁能给我一个提示,告诉我哪里出了错?
这是我的代码:
program InserElement(input, output);
{Has the user type in integers and forms a linked list out of them,
then inserts an element at the end of that linked list and prints the
linked list with the added new element}
{$mode objfpc}{$H+}
uses
{$IFDEF UNIX}{$IFDEF UseCThreads}
cthreads,
{$ENDIF}{$ENDIF}
Classes;
type
tRefList = ^tList;
tList = record
info : integer;
next : tRefList
end;
var
RefBeginning: tRefList;
RefEnd : tRefList;
Pointer : tRefList;
Number : integer;
procedure CreateList( var outRefBeginning: tRefList);
{ Creates a linear list through user input }
begin
readln(Number);
while Number <> 0 do
begin
new (Pointer);
Pointer^.info := Number;
Pointer^.next := outRefBeginning;
outRefBeginning := Pointer;
readln (Number)
end { while-loop }
end; {CreateList}
procedure InsertElement(inNumber : integer; var outRefBeginning : tRefList; var outRefEnd : tRefList);
{ Inserts a new element at the end of the list. outRefBeginning points to the first
element of that list, outRefEnd points to the last element of it. The Value of inNumber is
assigned to the record component info of the new element}
var
RefNew : tRefList;
begin
{ Create and initialise new element }
new(RefNew);
RefNew^.info := inNumber;
RefNew^.next := nil;
{ Insert element at the end of the linear list }
if outRefBeginning = nil then
begin
outRefBeginning := RefNew;
outRefEnd := RefNew
end
else
begin
outRefEnd^.next := RefNew;
outRefEnd := RefNew;
end;
end;{ InsertElement }
procedure PrintList;
{ Prints all elements of the linked list }
var
RefNew : tRefList;
begin
RefNew := RefBeginning;
while RefNew <> nil do
begin
writeln (RefNew^.info);
RefNew := RefNew^.next
end;
end;
begin
RefBeginning := nil;
RefEnd := RefBeginning;
CreateList(RefBeginning);
PrintList;
InsertElement(5,RefBeginning,RefEnd);
PrintList;
readln;
end.
[编辑]
对于任何感兴趣的人,我将粘贴下面更正的代码,我根据Tom答案中的建议更改了代码。
变化:
-
我删除了指针变量,因为不再需要它:
var
RefBeginning: tRefList;
RefEnd : tRefList;
Number : integer;
-
我改变了
procedure CreateList
类似于
procedure InsertElement
因为它不仅在
RefBeginning
,但也在
RefEnd
:
procedure CreateList(var outRefBeginning: tRefList; var OutRefEnd: tRefList);
{ Creates a linear list through user input }
var
RefNew : tRefList;`
begin
writeln('Please key in natural numbers. Key in 0 once you are done. ');
readln(Number);
while Number <> 0 do
begin
new (RefNew);
RefNew^.info := Number;
RefNew^.next := nil;
if outRefBeginning = nil then
begin
outRefBeginning := RefNew;
OutRefEnd := RefNew;
end
else
begin
outRefEnd^.next := RefNew;
outRefEnd := RefNew
end;
readln (Number)
end; { while-loop }
end; {CreateList}
最后但并非最不重要的是,以下是完整的代码:
program InserElement(input, output);
{Has the user type in integers and forms a linked list out of them,
then inserts an element at the end of that linked list and prints the
linked list with the added new element}
{$mode objfpc}{$H+}
uses
{$IFDEF UNIX}{$IFDEF UseCThreads}
cthreads,
{$ENDIF}{$ENDIF}
Classes;
type
tRefList = ^tList;
tList = record
info : integer;
next : tRefList
end;
var
RefBeginning: tRefList;
RefEnd : tRefList;
Number : integer;
procedure CreateList(var outRefBeginning: tRefList; var OutRefEnd: tRefList);
{ Creates a linear list through user input }
var
RefNew : tRefList;
begin
writeln('Please key in natural numbers. Key in 0 once you are done. ');
readln(Number);
while Number <> 0 do
begin
new (RefNew);
RefNew^.info := Number;
RefNew^.next := nil;
if outRefBeginning = nil then
begin
outRefBeginning := RefNew;
OutRefEnd := RefNew;
end
else
begin
outRefEnd^.next := RefNew;
outRefEnd := RefNew
end;
readln (Number)
end; { while-loop }
end; {CreateList}
procedure InsertElement(inNumber : integer; var outRefBeginning : tRefList; var outRefEnd : tRefList);
{ Inserts a new element at the end of the list. outRefBeginning points to the first
element of that list, outRefEnd points to the last element of it. The Value of inNumber is
assigned to the record component info of the new element}
var
RefNew : tRefList;
begin
{ Create and initialise new element }
new(RefNew);
RefNew^.info := inNumber;
RefNew^.next := nil;
{ Insert element at the end of the linear list }
if outRefBeginning = nil then
begin
outRefBeginning := RefNew;
outRefEnd := RefNew
end
else
begin
outRefEnd^.next := RefNew;
outRefEnd := RefNew;
end;
end;{ InsertElement }
procedure PrintList;
{ Prints all elements of the linked list }
var
RefNew : tRefList;
begin
RefNew := RefBeginning;
while RefNew <> nil do
begin
writeln (RefNew^.info);
RefNew := RefNew^.next
end;
end;
begin
RefBeginning := nil;
RefEnd := nil;
CreateList(RefBeginning, RefEnd);
InsertElement(5,RefBeginning,RefEnd);
PrintList;
readln;
end.
