如何为结构成员正确分配内存？

问题描述 投票：1回答：2

问题很不言自明。我想实现一个函数，该函数创建具有初始容量为[.C0]的动态数组和内部某些属性的结构。这是代码：

initial_capacity

这是#include <malloc.h> #include <stddef.h> #include <stdio.h> #include <stdlib.h> typedef struct IntVector { int *vector; unsigned int capacity; unsigned int size; } IntVector; IntVector *int_vector_new(size_t initial_capacity) { struct IntVector v = {calloc(initial_capacity, sizeof(int)), initial_capacity, 0}; IntVector* v_ptr = &v; return v_ptr; } 所说的：

valgrind --leak-check=full --show-leak-kinds=all --track-origins=yes -v ./debug

正如您所看到的，我已经连续三个小时试图解决此问题，但是没有任何进展。希望对您有所帮助。

c memory-management struct malloc calloc
2个回答
0
投票

我不知道可能会发生什么事情，因为目前您还没有任何代码可以显示调用的位置，但是我看到了一个大问题。您将返回一个指向在==1713== Memcheck, a memory error detector ==1713== Copyright (C) 2002-2017, and GNU GPL'd, by Julian Seward et al. ==1713== Using Valgrind-3.13.0 and LibVEX; rerun with -h for copyright info ==1713== Command: ./debug ==1713== --1713-- Valgrind options: --1713-- --leak-check=full --1713-- --show-leak-kinds=all --1713-- --track-origins=yes --1713-- -v --1713-- Contents of /proc/version: --1713-- Linux version 4.4.0-18362-Microsoft ([email protected]) (gcc version 5.4.0 (GCC) ) #476-Microsoft Fri Nov 01 16:53:00 PST 2019 --1713-- --1713-- Arch and hwcaps: AMD64, LittleEndian, amd64-cx16-lzcnt-rdtscp-sse3-avx-avx2-bmi --1713-- Page sizes: currently 4096, max supported 4096 --1713-- Valgrind library directory: /usr/lib/valgrind --1713-- Reading syms from /home/altbrace/IntVector/debug --1713-- Reading syms from /lib/x86_64-linux-gnu/ld-2.27.so --1713-- Considering /lib/x86_64-linux-gnu/ld-2.27.so .. --1713-- .. CRC mismatch (computed 1b7c895e wanted 2943108a) --1713-- Considering /usr/lib/debug/lib/x86_64-linux-gnu/ld-2.27.so .. --1713-- .. CRC is valid --1713-- Reading syms from /usr/lib/valgrind/memcheck-amd64-linux --1713-- Considering /usr/lib/valgrind/memcheck-amd64-linux .. --1713-- .. CRC mismatch (computed 41ddb025 wanted 9972f546) --1713-- object doesn't have a symbol table --1713-- object doesn't have a dynamic symbol table --1713-- Scheduler: using generic scheduler lock implementation. --1713-- Reading suppressions file: /usr/lib/valgrind/default.supp ==1713== embedded gdbserver: reading from /tmp/vgdb-pipe-from-vgdb-to-1713-by-altbrace-on-??? ==1713== embedded gdbserver: writing to /tmp/vgdb-pipe-to-vgdb-from-1713-by-altbrace-on-??? ==1713== embedded gdbserver: shared mem /tmp/vgdb-pipe-shared-mem-vgdb-1713-by-altbrace-on-??? ==1713== ==1713== TO CONTROL THIS PROCESS USING vgdb (which you probably ==1713== don't want to do, unless you know exactly what you're doing, ==1713== or are doing some strange experiment): ==1713== /usr/lib/valgrind/../../bin/vgdb --pid=1713 ...command... ==1713== ==1713== TO DEBUG THIS PROCESS USING GDB: start GDB like this ==1713== /path/to/gdb ./debug ==1713== and then give GDB the following command ==1713== target remote | /usr/lib/valgrind/../../bin/vgdb --pid=1713 ==1713== --pid is optional if only one valgrind process is running ==1713== ==1713== error calling PR_SET_PTRACER, vgdb might block --1713-- REDIR: 0x401f2f0 (ld-linux-x86-64.so.2:strlen) redirected to 0x580608c1 (???) --1713-- REDIR: 0x401f0d0 (ld-linux-x86-64.so.2:index) redirected to 0x580608db (???) --1713-- Reading syms from /usr/lib/valgrind/vgpreload_core-amd64-linux.so --1713-- Considering /usr/lib/valgrind/vgpreload_core-amd64-linux.so .. --1713-- .. CRC mismatch (computed 50df1b30 wanted 4800a4cf) --1713-- object doesn't have a symbol table --1713-- Reading syms from /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so --1713-- Considering /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so .. --1713-- .. CRC mismatch (computed f893b962 wanted 95ee359e) --1713-- object doesn't have a symbol table ==1713== WARNING: new redirection conflicts with existing -- ignoring it --1713-- old: 0x0401f2f0 (strlen ) R-> (0000.0) 0x580608c1 ??? --1713-- new: 0x0401f2f0 (strlen ) R-> (2007.0) 0x04c32db0 strlen --1713-- REDIR: 0x401d360 (ld-linux-x86-64.so.2:strcmp) redirected to 0x4c33ee0 (strcmp) --1713-- REDIR: 0x401f830 (ld-linux-x86-64.so.2:mempcpy) redirected to 0x4c374f0 (mempcpy) --1713-- Reading syms from /lib/x86_64-linux-gnu/libc-2.27.so --1713-- Considering /lib/x86_64-linux-gnu/libc-2.27.so .. --1713-- .. CRC mismatch (computed b1c74187 wanted 042cc048) --1713-- Considering /usr/lib/debug/lib/x86_64-linux-gnu/libc-2.27.so .. --1713-- .. CRC is valid --1713-- REDIR: 0x4edac70 (libc.so.6:memmove) redirected to 0x4a2a6e0 (_vgnU_ifunc_wrapper) --1713-- REDIR: 0x4ed9d40 (libc.so.6:strncpy) redirected to 0x4a2a6e0 (_vgnU_ifunc_wrapper) --1713-- REDIR: 0x4edaf50 (libc.so.6:strcasecmp) redirected to 0x4a2a6e0 (_vgnU_ifunc_wrapper) --1713-- REDIR: 0x4ed9790 (libc.so.6:strcat) redirected to 0x4a2a6e0 (_vgnU_ifunc_wrapper) --1713-- REDIR: 0x4ed9d70 (libc.so.6:rindex) redirected to 0x4a2a6e0 (_vgnU_ifunc_wrapper) --1713-- REDIR: 0x4edc7c0 (libc.so.6:rawmemchr) redirected to 0x4a2a6e0 (_vgnU_ifunc_wrapper) --1713-- REDIR: 0x4edade0 (libc.so.6:mempcpy) redirected to 0x4a2a6e0 (_vgnU_ifunc_wrapper) --1713-- REDIR: 0x4edac10 (libc.so.6:bcmp) redirected to 0x4a2a6e0 (_vgnU_ifunc_wrapper) --1713-- REDIR: 0x4ed9d00 (libc.so.6:strncmp) redirected to 0x4a2a6e0 (_vgnU_ifunc_wrapper) --1713-- REDIR: 0x4ed9800 (libc.so.6:strcmp) redirected to 0x4a2a6e0 (_vgnU_ifunc_wrapper) --1713-- REDIR: 0x4edad40 (libc.so.6:memset) redirected to 0x4a2a6e0 (_vgnU_ifunc_wrapper) --1713-- REDIR: 0x4ef80f0 (libc.so.6:wcschr) redirected to 0x4a2a6e0 (_vgnU_ifunc_wrapper) --1713-- REDIR: 0x4ed9ca0 (libc.so.6:strnlen) redirected to 0x4a2a6e0 (_vgnU_ifunc_wrapper) --1713-- REDIR: 0x4ed9870 (libc.so.6:strcspn) redirected to 0x4a2a6e0 (_vgnU_ifunc_wrapper) --1713-- REDIR: 0x4edafa0 (libc.so.6:strncasecmp) redirected to 0x4a2a6e0 (_vgnU_ifunc_wrapper) --1713-- REDIR: 0x4ed9840 (libc.so.6:strcpy) redirected to 0x4a2a6e0 (_vgnU_ifunc_wrapper) --1713-- REDIR: 0x4edb0e0 (libc.so.6:memcpy@@GLIBC_2.14) redirected to 0x4a2a6e0 (_vgnU_ifunc_wrapper) --1713-- REDIR: 0x4ed9da0 (libc.so.6:strpbrk) redirected to 0x4a2a6e0 (_vgnU_ifunc_wrapper) --1713-- REDIR: 0x4ed97c0 (libc.so.6:index) redirected to 0x4a2a6e0 (_vgnU_ifunc_wrapper) --1713-- REDIR: 0x4ed9c70 (libc.so.6:strlen) redirected to 0x4a2a6e0 (_vgnU_ifunc_wrapper) --1713-- REDIR: 0x4ee46c0 (libc.so.6:memrchr) redirected to 0x4a2a6e0 (_vgnU_ifunc_wrapper) --1713-- REDIR: 0x4edaff0 (libc.so.6:strcasecmp_l) redirected to 0x4a2a6e0 (_vgnU_ifunc_wrapper) --1713-- REDIR: 0x4edabe0 (libc.so.6:memchr) redirected to 0x4a2a6e0 (_vgnU_ifunc_wrapper) --1713-- REDIR: 0x4ef8eb0 (libc.so.6:wcslen) redirected to 0x4a2a6e0 (_vgnU_ifunc_wrapper) --1713-- REDIR: 0x4eda050 (libc.so.6:strspn) redirected to 0x4a2a6e0 (_vgnU_ifunc_wrapper) --1713-- REDIR: 0x4edaf20 (libc.so.6:stpncpy) redirected to 0x4a2a6e0 (_vgnU_ifunc_wrapper) --1713-- REDIR: 0x4edaef0 (libc.so.6:stpcpy) redirected to 0x4a2a6e0 (_vgnU_ifunc_wrapper) --1713-- REDIR: 0x4edc7f0 (libc.so.6:strchrnul) redirected to 0x4a2a6e0 (_vgnU_ifunc_wrapper) --1713-- REDIR: 0x4edb040 (libc.so.6:strncasecmp_l) redirected to 0x4a2a6e0 (_vgnU_ifunc_wrapper) --1713-- REDIR: 0x4fca3c0 (libc.so.6:__strrchr_avx2) redirected to 0x4c32730 (rindex) --1713-- REDIR: 0x4ed6030 (libc.so.6:calloc) redirected to 0x4c31a70 (calloc) --1713-- REDIR: 0x4ed3950 (libc.so.6:free) redirected to 0x4c30cd0 (free) ==1713== ==1713== HEAP SUMMARY: ==1713== in use at exit: 20 bytes in 1 blocks ==1713== total heap usage: 1 allocs, 0 frees, 20 bytes allocated ==1713== ==1713== Searching for pointers to 1 not-freed blocks ==1713== Checked 69,336 bytes ==1713== ==1713== 20 bytes in 1 blocks are definitely lost in loss record 1 of 1 ==1713== at 0x4C31B25: calloc (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so) ==1713== by 0x1086F2: int_vector_new (IntVector.c:13) ==1713== by 0x1086BB: main (main.c:8) ==1713== ==1713== LEAK SUMMARY: ==1713== definitely lost: 20 bytes in 1 blocks ==1713== indirectly lost: 0 bytes in 0 blocks ==1713== possibly lost: 0 bytes in 0 blocks ==1713== still reachable: 0 bytes in 0 blocks ==1713== suppressed: 0 bytes in 0 blocks ==1713== ==1713== ERROR SUMMARY: 1 errors from 1 contexts (suppressed: 0 from 0) ==1713== ERROR SUMMARY: 1 errors from 1 contexts (suppressed: 0 from 0) 中创建的值的指针，因此一旦该函数返回指向（int_vector_new）的局部变量，就会消失。

您可以为v分配内存，就像这样：v。

然后使用IntVector* v = malloc(sizeof(IntVector));语法设置每个字段。像这样：

->

由于valgrind抱怨泄漏，所以我猜您稍后不会在代码中释放IntVector* v = malloc(sizeof(IntVector)); v->vector = calloc(initial_capacity, sizeof(int)); v->capacity = initial_capacity; v->size = 0; return v; 。释放内存将解决有关内存泄漏的投诉。使用vector分配malloc后，您将需要释放v返回的所有值。

3
投票

功能

int_vector_new

返回一个指向声明的局部变量的指针，如

IntVector *int_vector_new(size_t initial_capacity) {
        struct IntVector v = {calloc(initial_capacity, sizeof(int)),
                               initial_capacity, 0};
        IntVector* v_ptr = &v;
        return v_ptr;
}

因此，退出函数后，指针具有无效值，因为指向的对象不再存在。

要么动态分配结构类型的对象，然后将指针返回给分配的内存。或按值将对象v本身返回给函数的调用者。

例如

struct IntVector v

或

IntVector int_vector_new(size_t initial_capacity) {
        struct IntVector v = {calloc(initial_capacity, sizeof(int)),
                               initial_capacity, 0};
        return v;
}

您可以添加检查是否成功分配了内存。

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