【发布时间】：2015-04-19 20:16:24
【问题描述】：
我一直在开发一个 Fortran 95 程序，它试图猜测您在想什么。它需要一个文件，其行格式为id label question yes no:
9
1 . Is_it_a_living_thing? 2 7
2 . Can_it_walk? 3 6
3 . Does_it_meow? 4 5
4 a_cat . 0 0
5 David_Mitchell . 0 0
6 a_bacteria . 0 0
7 . Is_it_electrical? 8 9
8 a_toaster . 0 0
9 hair_gel . 0 0
下划线的原因是我制作的这个程序的 C 实现，它在阅读时很高兴与 Fortran 的格式配合使用。代码如下：
module types
implicit none
type node
character (len = 32) :: label
character (len = 128) :: question
type(node), pointer :: yes, no
end type node
end module types
program pangolins
use types
implicit none
!type(node), allocatable :: nodes(:)
type(node), pointer :: head, current
! Program
head => parseFile()
nullify(current)
call freeAll(head)
stop
contains
function parseFile() result(head)
implicit none
type(node), pointer :: nodes(:)
type(node), pointer :: head
integer :: i, n, thisN, thisYes, thisNo
character (len = 32) :: thisLabel
character (len = 128) :: thisQuestion
open(10, file = './file1')
read(10, *) n
write(*, *) 'Nodes: ', n
allocate(nodes(n))
do i = 1, n
read(10, *) thisN, thisLabel, thisQuestion, thisYes, thisNo
write (*,'(a24,a64,i4,i4)') thisLabel, thisQuestion, thisYes, thisNo
nodes(i)%label = thisLabel
nodes(i)%question = thisQuestion
if (thisYes .eq. 0) then
nullify(nodes(i)%yes)
else
nodes(i)%yes => nodes(thisYes)
end if
if (thisNo .eq. 0) then
nullify(nodes(i)%no)
else
nodes(i)%no => nodes(thisNo)
end if
end do
head => nodes(1)
end function parseFile
recursive subroutine freeAll(head)
implicit none
type(node), pointer :: head
if (associated(head%yes)) then
call freeAll(head%yes)
end if
if (associated(head%no)) then
call freeAll(head%no)
end if
write (*,'(a24,a64)') head%label, head%question
deallocate(head)
end subroutine freeAll
end program pangolins
当前代码只是初始化数组，然后尝试再次干净地释放它。
该问题与指向数组的指针和数组元素有关。我的函数parseFile 通过首先将文件中的节点解析为指针数组并通过数组中的索引指向是和否指针，然后返回始终是树的头部的第一个元素，从而使树的组织变得容易。这在 C 中很直观，这就是我的出发点。
当我运行此代码时，freeAll() 中对 deallocate() 的第二次调用会导致双重空闲段错误。
我怀疑我将此与使用指针数组的 C 版本混淆了，因此尽管我将起始节点初始化为数组，但我可以使用按顺序遍历作为树一次释放每个指针自初始化以来可能已经变大，然后最终释放数组。这是我一直试图从 C 移植的函数：
...
node_t* readFile(FILE* inFile)
{
int noOfNodes;
fscanf(inFile, "%d", &noOfNodes);
node_t** nodes = (node_t**) malloc(sizeof(node_t*) * noOfNodes);
for (int i = 0; i < noOfNodes; i++)
nodes[i] = (node_t*) malloc(sizeof(node_t));
char* nodeLabel = (char*) malloc(sizeof(char) * MAX_LABEL_SIZE);
char* nodeQuestion = (char*) malloc(sizeof(char) * MAX_QUESTION_SIZE);
...
我错过了什么？回溯如下：
$ gfortran -pedantic -Wall -ggdb -fbacktrace -fcheck=all -o pangolins pangolins.f95
pangolins.f95:65.6:
head => nodes(1)
1
Warning: Pointer at (1) in pointer assignment might outlive the pointer target
$ ./pangolins
Nodes: 9
. Is_it_a_living_thing? 2 7
. Can_it_walk? 3 6
. Does_it_meow? 4 5
a_cat . 0 0
David_Mitchell . 0 0
a_bacteria . 0 0
. Is_it_electrical? 8 9
a_toaster . 0 0
hair_gel . 0 0
a_cat .
*** Error in `./pangolins': double free or corruption (out): 0x0000000000858700 ***
======= Backtrace: =========
/lib64/libc.so.6[0x3055875a4f]
/lib64/libc.so.6[0x305587cd78]
./pangolins[0x400d7d]
./pangolins[0x400c70]
./pangolins[0x400c70]
./pangolins[0x400c70]
./pangolins[0x400ddf]
./pangolins[0x4018b6]
/lib64/libc.so.6(__libc_start_main+0xf5)[0x3055821d65]
./pangolins[0x400b69]
======= Memory map: ========
00400000-00402000 r-xp 00000000 08:03 5636403 /home/adam/utils/fortran/pangolins
00602000-00603000 r--p 00002000 08:03 5636403 /home/adam/utils/fortran/pangolins
00603000-00604000 rw-p 00003000 08:03 5636403 /home/adam/utils/fortran/pangolins
00853000-00874000 rw-p 00000000 00:00 0 [heap]
3055400000-3055420000 r-xp 00000000 08:03 4459030 /usr/lib64/ld-2.18.so
305561f000-3055620000 r--p 0001f000 08:03 4459030 /usr/lib64/ld-2.18.so
3055620000-3055621000 rw-p 00020000 08:03 4459030 /usr/lib64/ld-2.18.so
3055621000-3055622000 rw-p 00000000 00:00 0
3055800000-30559b4000 r-xp 00000000 08:03 4499543 /usr/lib64/libc-2.18.so
30559b4000-3055bb3000 ---p 001b4000 08:03 4499543 /usr/lib64/libc-2.18.so
3055bb3000-3055bb7000 r--p 001b3000 08:03 4499543 /usr/lib64/libc-2.18.so
3055bb7000-3055bb9000 rw-p 001b7000 08:03 4499543 /usr/lib64/libc-2.18.so
3055bb9000-3055bbe000 rw-p 00000000 00:00 0
3056800000-3056905000 r-xp 00000000 08:03 4460722 /usr/lib64/libm-2.18.so
3056905000-3056b05000 ---p 00105000 08:03 4460722 /usr/lib64/libm-2.18.so
3056b05000-3056b06000 r--p 00105000 08:03 4460722 /usr/lib64/libm-2.18.so
3056b06000-3056b07000 rw-p 00106000 08:03 4460722 /usr/lib64/libm-2.18.so
3057400000-3057415000 r-xp 00000000 08:03 4499572 /usr/lib64/libgcc_s-4.8.3-20140911.so.1
3057415000-3057614000 ---p 00015000 08:03 4499572 /usr/lib64/libgcc_s-4.8.3-20140911.so.1
3057614000-3057615000 r--p 00014000 08:03 4499572 /usr/lib64/libgcc_s-4.8.3-20140911.so.1
3057615000-3057616000 rw-p 00015000 08:03 4499572 /usr/lib64/libgcc_s-4.8.3-20140911.so.1
7fcb37dc5000-7fcb37dc9000 rw-p 00000000 00:00 0
7fcb37dc9000-7fcb37e04000 r-xp 00000000 08:03 4471039 /usr/lib64/libquadmath.so.0.0.0
7fcb37e04000-7fcb38003000 ---p 0003b000 08:03 4471039 /usr/lib64/libquadmath.so.0.0.0
7fcb38003000-7fcb38004000 r--p 0003a000 08:03 4471039 /usr/lib64/libquadmath.so.0.0.0
7fcb38004000-7fcb38005000 rw-p 0003b000 08:03 4471039 /usr/lib64/libquadmath.so.0.0.0
7fcb38005000-7fcb38006000 rw-p 00000000 00:00 0
7fcb38006000-7fcb38125000 r-xp 00000000 08:03 4470960 /usr/lib64/libgfortran.so.3.0.0
7fcb38125000-7fcb38325000 ---p 0011f000 08:03 4470960 /usr/lib64/libgfortran.so.3.0.0
7fcb38325000-7fcb38326000 r--p 0011f000 08:03 4470960 /usr/lib64/libgfortran.so.3.0.0
7fcb38326000-7fcb38328000 rw-p 00120000 08:03 4470960 /usr/lib64/libgfortran.so.3.0.0
7fcb3834b000-7fcb3834d000 rw-p 00000000 00:00 0
7ffdefd3b000-7ffdefd5c000 rw-p 00000000 00:00 0 [stack]
7ffdefd8e000-7ffdefd90000 r--p 00000000 00:00 0 [vvar]
7ffdefd90000-7ffdefd92000 r-xp 00000000 00:00 0 [vdso]
ffffffffff600000-ffffffffff601000 r-xp 00000000 00:00 0 [vsyscall]
Program received signal SIGABRT: Process abort signal.
Backtrace for this error:
#0 0x7FCB3801F497
#1 0x7FCB3801FADE
#2 0x30558358EF
#3 0x3055835877
#4 0x3055836F67
#5 0x3055875A53
#6 0x305587CD77
#7 0x400D7C in freeall at pangolins.f95:82 (discriminator 2)
#8 0x400C6F in freeall at pangolins.f95:74
#9 0x400C6F in freeall at pangolins.f95:74
#10 0x400C6F in freeall at pangolins.f95:74
#11 0x400DDE in pangolins at pangolins.f95:23
Aborted (core dumped)
第一次解除分配有效，但随后的解除分配会导致问题。请注意write 打印在deallocate() 上方的a_cat 的第二个打印。
【问题讨论】：
-
抱歉，我错过了这个问题。这不是问题的原因。我将添加一个回溯。
标签： c pointers fortran dynamic-memory-allocation