c - 如何在函数中缩短数组？ (动态数组，内存泄漏)

Question

我有一个动态分配的数组，比方说:

double *values = malloc(sizeof(double)*3);
values[0] = 0.9988;
values[1] = 0.0540;
values[2] = 0.0100;

然后，我有一个函数可以缩短我的数组，所以我在新数组中只有原始数组的最后两个元素。所以，我的结果数组应该是:

values[1] = 0.0540;
values[2] = 0.0100;

如您所见，我只从原始数组中复制了最后两个值。函数应该返回一个新的大小(旧大小 - 1，我只删除了第一个元素)。但是通过我的代码，我得到:

values[0] = 0.0000
values[1] = 0.0540

代替:

values[1] = 0.0540;
values[2] = 0.0100;

此外，我还有一些内存泄漏:

==5876== Memcheck, a memory error detector
==5876== Copyright (C) 2002-2012, and GNU GPL'd, by Julian Seward et al.
==5876== Using Valgrind-3.8.1 and LibVEX; rerun with -h for copyright info
==5876== Command: ./Untitled3
==5876== 
--5876-- Valgrind options:
--5876--    --suppressions=/usr/lib/valgrind/debian-libc6-dbg.supp
--5876--    --tool=memcheck
--5876--    --track-origins=yes
--5876--    --leak-check=yes
--5876--    --show-reachable=yes
--5876--    -v
--5876--    --track-fds=yes
--5876-- Contents of /proc/version:
--5876--   Linux version 3.8.0-34-generic (buildd@roseapple) (gcc version 4.7.3 (Ubuntu/Linaro 4.7.3-1ubuntu1) ) #49-Ubuntu SMP Tue Nov 12 18:00:10 UTC 2013
--5876-- Arch and hwcaps: AMD64, amd64-sse3-cx16-avx
--5876-- Page sizes: currently 4096, max supported 4096
--5876-- Valgrind library directory: /usr/lib/valgrind
--5876-- Reading syms from /home/yak/test/Untitled3
--5876-- Reading syms from /lib/x86_64-linux-gnu/ld-2.17.so
--5876--   Considering /lib/x86_64-linux-gnu/ld-2.17.so ..
--5876--   .. CRC mismatch (computed 5d246d73 wanted cbf42dbe)
--5876--   Considering /usr/lib/debug/lib/x86_64-linux-gnu/ld-2.17.so ..
--5876--   .. CRC is valid
--5876--   Considering /usr/lib/debug/lib/x86_64-linux-gnu/ld-2.17.so ..
--5876--   .. CRC is valid
--5876-- Reading syms from /usr/lib/valgrind/memcheck-amd64-linux
--5876--   Considering /usr/lib/valgrind/memcheck-amd64-linux ..
--5876--   .. CRC mismatch (computed 8dadd6e3 wanted 096f8488)
--5876--    object doesn't have a symbol table
--5876--    object doesn't have a dynamic symbol table
--5876-- Scheduler: using generic scheduler lock implementation.
--5876-- Reading suppressions file: /usr/lib/valgrind/debian-libc6-dbg.supp
--5876-- Reading suppressions file: /usr/lib/valgrind/default.supp
==5876== embedded gdbserver: reading from /tmp/vgdb-pipe-from-vgdb-to-5876-by-yak-on-???
==5876== embedded gdbserver: writing to   /tmp/vgdb-pipe-to-vgdb-from-5876-by-yak-on-???
==5876== embedded gdbserver: shared mem   /tmp/vgdb-pipe-shared-mem-vgdb-5876-by-yak-on-???
==5876== 
==5876== TO CONTROL THIS PROCESS USING vgdb (which you probably
==5876== don't want to do, unless you know exactly what you're doing,
==5876== or are doing some strange experiment):
==5876==   /usr/lib/valgrind/../../bin/vgdb --pid=5876 ...command...
==5876== 
==5876== TO DEBUG THIS PROCESS USING GDB: start GDB like this
==5876==   /path/to/gdb ./Untitled3
==5876== and then give GDB the following command
==5876==   target remote | /usr/lib/valgrind/../../bin/vgdb --pid=5876
==5876== --pid is optional if only one valgrind process is running
==5876== 
--5876-- REDIR: 0x4018f40 (strlen) redirected to 0x3806c7e1 (???)
--5876-- Reading syms from /usr/lib/valgrind/vgpreload_core-amd64-linux.so
--5876--   Considering /usr/lib/valgrind/vgpreload_core-amd64-linux.so ..
--5876--   .. CRC mismatch (computed 7ae7d82a wanted 34ea3d89)
--5876--    object doesn't have a symbol table
--5876-- Reading syms from /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so
--5876--   Considering /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so ..
--5876--   .. CRC mismatch (computed 272279e5 wanted bc83f658)
--5876--    object doesn't have a symbol table
--5876-- REDIR: 0x4018db0 (index) redirected to 0x4c2d440 (index)
--5876-- REDIR: 0x4018e30 (strcmp) redirected to 0x4c2e480 (strcmp)
--5876-- Reading syms from /lib/x86_64-linux-gnu/libc-2.17.so
--5876--   Considering /lib/x86_64-linux-gnu/libc-2.17.so ..
--5876--   .. CRC mismatch (computed 08d04634 wanted e58fe8a7)
--5876--   Considering /usr/lib/debug/lib/x86_64-linux-gnu/libc-2.17.so ..
--5876--   .. CRC is valid
--5876--   Considering /usr/lib/debug/lib/x86_64-linux-gnu/libc-2.17.so ..
--5876--   .. CRC is valid
--5876-- REDIR: 0x4ec1a30 (strcasecmp) redirected to 0x4a25710 (_vgnU_ifunc_wrapper)
--5876-- REDIR: 0x4ebddc0 (strnlen) redirected to 0x4a25710 (_vgnU_ifunc_wrapper)
--5876-- REDIR: 0x4ec3d00 (strncasecmp) redirected to 0x4a25710 (_vgnU_ifunc_wrapper)
--5876-- REDIR: 0x4ec0840 (memset) redirected to 0x4a25710 (_vgnU_ifunc_wrapper)
--5876-- REDIR: 0x4ec07f0 (memcpy@GLIBC_2.2.5) redirected to 0x4a25710 (_vgnU_ifunc_wrapper)
--5876-- REDIR: 0x4ebf7b0 (__GI_strrchr) redirected to 0x4c2d260 (__GI_strrchr)
--5876-- REDIR: 0x4eb7520 (malloc) redirected to 0x4c2cd10 (malloc)
--5876-- REDIR: 0x4ec7bd0 (strchrnul) redirected to 0x4c2fea0 (strchrnul)
--5876-- REDIR: 0x4ebdce0 (__GI_strlen) redirected to 0x4c2d7c0 (__GI_strlen)
arr[0] = 0.9988
--5876-- REDIR: 0x4eb79b0 (free) redirected to 0x4c2ba00 (free)
arr[1] = 0.0540
arr[2] = 0.0100


==5876== Invalid read of size 8
==5876==    at 0x40063D: print_out_an_array_f (in /home/yak/test/Untitled3)
==5876==    by 0x40078C: main (in /home/yak/test/Untitled3)
==5876==  Address 0x51fd040 is 0 bytes inside a block of size 24 free'd
==5876==    at 0x4C2BA6C: free (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so)
==5876==    by 0x4006E4: shortArray (in /home/yak/test/Untitled3)
==5876==    by 0x400778: main (in /home/yak/test/Untitled3)
==5876== 
arr[0] = 0.9988
arr[1] = 0.0540
==5876== 
==5876== FILE DESCRIPTORS: 3 open at exit.
==5876== Open file descriptor 2: /dev/pts/4
==5876==    <inherited from parent>
==5876== 
==5876== Open file descriptor 1: /dev/pts/4
==5876==    <inherited from parent>
==5876== 
==5876== Open file descriptor 0: /dev/pts/4
==5876==    <inherited from parent>
==5876== 
==5876== 
==5876== HEAP SUMMARY:
==5876==     in use at exit: 16 bytes in 1 blocks
==5876==   total heap usage: 2 allocs, 1 frees, 40 bytes allocated
==5876== 
==5876== Searching for pointers to 1 not-freed blocks
==5876== Checked 78,504 bytes
==5876== 
==5876== 16 bytes in 1 blocks are definitely lost in loss record 1 of 1
==5876==    at 0x4C2CD7B: malloc (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so)
==5876==    by 0x40068D: shortArray (in /home/yak/test/Untitled3)
==5876==    by 0x400778: main (in /home/yak/test/Untitled3)
==5876== 
==5876== LEAK SUMMARY:
==5876==    definitely lost: 16 bytes in 1 blocks
==5876==    indirectly lost: 0 bytes in 0 blocks
==5876==      possibly lost: 0 bytes in 0 blocks
==5876==    still reachable: 0 bytes in 0 blocks
==5876==         suppressed: 0 bytes in 0 blocks
==5876== 
==5876== ERROR SUMMARY: 3 errors from 2 contexts (suppressed: 2 from 2)
==5876== 
==5876== 2 errors in context 1 of 2:
==5876== Invalid read of size 8
==5876==    at 0x40063D: print_out_an_array_f (in /home/yak/test/Untitled3)
==5876==    by 0x40078C: main (in /home/yak/test/Untitled3)
==5876==  Address 0x51fd040 is 0 bytes inside a block of size 24 free'd
==5876==    at 0x4C2BA6C: free (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so)
==5876==    by 0x4006E4: shortArray (in /home/yak/test/Untitled3)
==5876==    by 0x400778: main (in /home/yak/test/Untitled3)
==5876== 
--5876-- 
--5876-- used_suppression:      2 dl-hack3-cond-1
==5876== 
==5876== ERROR SUMMARY: 3 errors from 2 contexts (suppressed: 2 from 2)

使用这段代码:

#include <stdio.h>

void print_out_an_array_f(unsigned int n, double *arr)
{
    unsigned int i = 0;
    for(i=0; i<n; i++)
        printf("arr[%d] = %.4f\n", i, arr[i]);
}

int shortArray(int n, double *arr)
{
    int i;
    double *tmp = malloc(sizeof(double) * (n-1));
    for(i=1; i<n; i++)
    {
        tmp[i-1] = arr[i];
        //printf("\ntmp[%d] = %f", i-1, tmp[i-1]);
        //printf("\narr[%d] = %f \n", i-1, arr[i]);
    }

    free(arr);
    arr = tmp;

    return n-1;
}

int main(int argc, char **argv)
{
    double *values = malloc(sizeof(double)*3);
    values[0] = 0.9988;
    values[1] = 0.0540;
    values[2] = 0.0100;

    print_out_an_array_f(3, values);

    printf("\n\n");

    int m = shortArray(3, values);

    print_out_an_array_f(m, values);

    //free(values);

    return 0;
}

但是当我释放 value 数组时(在 main 中的 return 0; 之前)，我遇到了其他问题:

*** Error in `./Untitled3': double free or corruption (fasttop): 0x0000000001d12010 ***
======= Backtrace: =========
/lib/x86_64-linux-gnu/libc.so.6(+0x80a46)[0x7f40adfa6a46]
./Untitled3[0x400799]
/lib/x86_64-linux-gnu/libc.so.6(__libc_start_main+0xf5)[0x7f40adf47ea5]
./Untitled3[0x400549]
======= Memory map: ========
00400000-00401000 r-xp 00000000 08:08 9440662                            /home/yak/test/Untitled3
00600000-00601000 r--p 00000000 08:08 9440662                            /home/yak/test/Untitled3
00601000-00602000 rw-p 00001000 08:08 9440662                            /home/yak/test/Untitled3
01d12000-01d33000 rw-p 00000000 00:00 0                                  [heap]
7f40add10000-7f40add24000 r-xp 00000000 08:06 16780936                   /lib/x86_64-linux-gnu/libgcc_s.so.1
7f40add24000-7f40adf24000 ---p 00014000 08:06 16780936                   /lib/x86_64-linux-gnu/libgcc_s.so.1
7f40adf24000-7f40adf25000 r--p 00014000 08:06 16780936                   /lib/x86_64-linux-gnu/libgcc_s.so.1
7f40adf25000-7f40adf26000 rw-p 00015000 08:06 16780936                   /lib/x86_64-linux-gnu/libgcc_s.so.1
7f40adf26000-7f40ae0e5000 r-xp 00000000 08:06 16779220                   /lib/x86_64-linux-gnu/libc-2.17.so
7f40ae0e5000-7f40ae2e4000 ---p 001bf000 08:06 16779220                   /lib/x86_64-linux-gnu/libc-2.17.so
7f40ae2e4000-7f40ae2e8000 r--p 001be000 08:06 16779220                   /lib/x86_64-linux-gnu/libc-2.17.so
7f40ae2e8000-7f40ae2ea000 rw-p 001c2000 08:06 16779220                   /lib/x86_64-linux-gnu/libc-2.17.so
7f40ae2ea000-7f40ae2ef000 rw-p 00000000 00:00 0 
7f40ae2ef000-7f40ae312000 r-xp 00000000 08:06 16779153                   /lib/x86_64-linux-gnu/ld-2.17.so
7f40ae4e9000-7f40ae4ec000 rw-p 00000000 00:00 0 
7f40ae50d000-7f40ae511000 rw-p 00000000 00:00 0 
7f40ae511000-7f40ae512000 r--p 00022000 08:06 16779153                   /lib/x86_64-linux-gnu/ld-2.17.so
7f40ae512000-7f40ae514000 rw-p 00023000 08:06 16779153                   /lib/x86_64-linux-gnu/ld-2.17.so
7fff3fc3b000-7fff3fc5c000 rw-p 00000000 00:00 0                          [stack]
7fff3fdfe000-7fff3fe00000 r-xp 00000000 00:00 0                          [vdso]
ffffffffff600000-ffffffffff601000 r-xp 00000000 00:00 0                  [vsyscall]

Answer 1

赋值 arr = tmp 仅更改局部变量 arr。它不会更改调用者中的指针。您看到的错误源于 main() 在旧数组指针被释放后继续使用它。

如果您想更改调用方的 int 变量，您需要编写一个接受 int * 的函数。此处您想要更改调用方的 double *，因此您的函数应该采用 double **。

int shortArray(int n, double **arr)
{
    int i;
    double *tmp = malloc(sizeof(double) * (n-1));
    for(i=1; i<n; i++)
    {
        tmp[i-1] = (*arr)[i];
        //printf("\ntmp[%d] = %f", i-1, tmp[i-1]);
        //printf("\narr[%d] = %f \n", i-1, arr[i]);
    }

    free(*arr);
    *arr = tmp;

    return n-1;
}

然后将调用更改为:

int m = shortArray(3, &values);