Question

我在realloc发生此错误，这只发生在我学校的实验室计算机上而不是我的计算机上。

在这个程序中，我将行号存储在File_Node结构中。 File_Node是链接列表的一部分，每个节点包含文件中的文件路径字符串和数组行号。

此程序正常工作，直到需要存储的行号太多（> 3000）。

以下是我的代码的相关部分：

           if ((token = strtok(NULL, delim)) != NULL) {
                    char *endptr = NULL;
                    int *linenum_tmp = NULL;
                    long line_number;
                    errno = 0;
                    line_number = strtol(token, &endptr, 10);

                    if (errno == ERANGE) {
                            exit_program("Integer overflow.");
                    }

                    if (*endptr != '\0' || endptr == token || line_number < 0) {
                            exit_program("Cannot parse line number input.");
                    }
                    if (tail->line_numbers == NULL) {
                            tail->line_numbers = malloc(num_array_sz * sizeof(int));
                    }
                    if (counter == num_array_sz) { //Area of interest
                            num_array_sz *= 2;
                            if ((linenum_tmp = realloc(tail->line_numbers, sizeof(int) * num_array_sz)) == NULL) { 
                                    exit_program("Error in realloc."); 
                            }
                    }
                    *(tail->line_numbers + counter - 1) = line_number;

            } else {
                    exit_program("Cannot parse line number input.");
            }
            counter++;

上面的代码是一个更大的while循环的一部分，它包含更多的行，但我会在必要时发布它。这就是为什么底部有counter++的原因。每当num_array_sz表示存储的行数达到counter时，我的num_array_sz的大小基本上翻了一倍，256初始化为==1579== Memcheck, a memory error detector ==1579== Copyright (C) 2002-2012, and GNU GPL'd, by Julian Seward et al. ==1579== Using Valgrind-3.8.1 and LibVEX; rerun with -h for copyright info ==1579== Command: ./rgpp_v2 -w the -b -n ==1579== ==1579== Invalid write of size 4 ==1579== at 0x40110E: process_input (rgpp_v2.c:181) ==1579== by 0x400DCC: main (rgpp_v2.c:103) ==1579== Address 0x51e0b9c is 1,020 bytes inside a block of size 1,024 free'd ==1579== at 0x4C29B7E: realloc (in /usr/lib64/valgrind/vgpreload_memcheck-amd64-linux.so) ==1579== by 0x4010DD: process_input (rgpp_v2.c:177) ==1579== by 0x400DCC: main (rgpp_v2.c:103) ==1579== ==1579== Invalid free() / delete / delete[] / realloc() ==1579== at 0x4C29B7E: realloc (in /usr/lib64/valgrind/vgpreload_memcheck-amd64-linux.so) ==1579== by 0x4010DD: process_input (rgpp_v2.c:177) ==1579== by 0x400DCC: main (rgpp_v2.c:103) ==1579== Address 0x51e07a0 is 0 bytes inside a block of size 1,024 free'd ==1579== at 0x4C29B7E: realloc (in /usr/lib64/valgrind/vgpreload_memcheck-amd64-linux.so) ==1579== by 0x4010DD: process_input (rgpp_v2.c:177) ==1579== by 0x400DCC: main (rgpp_v2.c:103) ==1579== Error in realloc. ==1579== ==1579== HEAP SUMMARY: ==1579== in use at exit: 3,477 bytes in 9 blocks ==1579== total heap usage: 12 allocs, 3 frees, 8,717 bytes allocated ==1579== ==1579== LEAK SUMMARY: ==1579== definitely lost: 2,048 bytes in 1 blocks ==1579== indirectly lost: 0 bytes in 0 blocks ==1579== possibly lost: 0 bytes in 0 blocks ==1579== still reachable: 1,429 bytes in 8 blocks ==1579== suppressed: 0 bytes in 0 blocks ==1579== Rerun with --leak-check=full to see details of leaked memory ==1579== ==1579== For counts of detected and suppressed errors, rerun with: -v ==1579== ERROR SUMMARY: 34 errors from 2 contexts (suppressed: 2 from 2)。

在我自己的计算机上，我用比学校计算机更多的输入来测试它，它运行得很完美。

我很好奇这是因为我学校的计算机上的ram有限还是平台上的差异。

这是我在学校计算机上运行的valgrind输出：

realloc

这些错误指向{{1}}行。

Answer 1

您未正确使用realloc。

linenum_tmp = realloc(tail->line_numbers, ....
...
*(tail->line_numbers + counter - 1) = ...

如果realloc需要重新分配内存，则传递给它的指针为freed。然后，您继续使用{em>旧的，已释放的值tail->line_numbers。

您必须始终使用realloc的返回值。

我认为你想要的是：

tail->line_numbers = realloc(tail->line_numbers, ...

其次，您误解了valgrind告诉您的内容。

==1579== Invalid write of size 4
==1579==    at 0x40110E: process_input (rgpp_v2.c:181)
==1579==    by 0x400DCC: main (rgpp_v2.c:103)
==1579==  Address 0x51e0b9c is 1,020 bytes inside a block of size 1,024 free'd
==1579==    at 0x4C29B7E: realloc (in /usr/lib64/valgrind/vgpreload_memcheck-amd64-linux.so)
==1579==    by 0x4010DD: process_input (rgpp_v2.c:177)
==1579==    by 0x400DCC: main (rgpp_v2.c:103)

它的含义是：在功能process_input（rgpp_v2.c的第181行）中，您正在访问之前free d的内存。供您参考，之前已由realloc释放，process_input在rgpp_v2.c的第177行调用。{/ p>

Answer 2

            if (counter == num_array_sz) { //Area of interest
                    num_array_sz *= 2;
                    if ((linenum_tmp = realloc(tail->line_numbers, sizeof(int) * num_array_sz)) == NULL) { 
                            exit_program("Error in realloc."); 
                    }
            }
            *(tail->line_numbers + counter - 1) = line_number;

您需要使用realloc的结果更新工作变量，如下所示：

            if (counter == num_array_sz) { //Area of interest
                    num_array_sz *= 2;
                    if ((linenum_tmp = realloc(tail->line_numbers, sizeof(int) * num_array_sz)) == NULL) { 
                            exit_program("Error in realloc."); 
                    }
            }

            tail->line_numbers = linenum_tmp; // <---!

            *(tail->line_numbers + counter - 1) = line_number;

realloc：下一个大小错误无效

2 个答案: