第十四章 内存操作API
1.
- 运行程序无事发生
#include <sys/types.h>
#include <unistd.h>
#include <iostream>
using namespace std;
int main()
{
int *x = NULL;
free(x);
return 0;
}
2.
gdb输出
(gdb) run
Starting program: /home/acs/code/chapter14/null
warning: Error disabling address space randomization: Operation not permitted
[Inferior 1 (process 66702) exited normally]
3.
valgrind输出，没有检测出什么错误
==66806== Memcheck, a memory error detector
==66806== Copyright (C) 2002-2017, and GNU GPL'd, by Julian Seward et al.
==66806== Using Valgrind-3.15.0 and LibVEX; rerun with -h for copyright info
==66806== Command: ./null
==66806==
==66806==
==66806== HEAP SUMMARY:
==66806== in use at exit: 0 bytes in 0 blocks
==66806== total heap usage: 1 allocs, 1 frees, 72,704 bytes allocated
==66806==
==66806== All heap blocks were freed -- no leaks are possible
==66806==
==66806== For lists of detected and suppressed errors, rerun with: -s
==66806== ERROR SUMMARY: 0 errors from 0 contexts (suppressed: 0 from 0)
4.
- 实验代码
#include <sys/types.h>
#include <unistd.h>
#include <iostream>
using namespace std;
int main()
{
int *x = (int*)malloc(sizeof(int));
return 0;
}
- gdb输出
(gdb) run
Starting program: /home/acs/code/chapter14/code4
warning: Error disabling address space randomization: Operation not permitted
[Inferior 1 (process 66903) exited normally]
- valgrind输出
==66911== Memcheck, a memory error detector
==66911== Copyright (C) 2002-2017, and GNU GPL'd, by Julian Seward et al.
==66911== Using Valgrind-3.15.0 and LibVEX; rerun with -h for copyright info
==66911== Command: ./code4
==66911==
==66911==
==66911== HEAP SUMMARY:
==66911== in use at exit: 4 bytes in 1 blocks
==66911== total heap usage: 2 allocs, 1 frees, 72,708 bytes allocated
==66911==
==66911== 4 bytes in 1 blocks are definitely lost in loss record 1 of 1
==66911== at 0x483B7F3: malloc (in /usr/lib/x86_64-linux-gnu/valgrind/vgpreload_memcheck-amd64-linux.so)
==66911== by 0x10919E: main (code4.cpp:7)
==66911==
==66911== LEAK SUMMARY:
==66911== definitely lost: 4 bytes in 1 blocks
==66911== indirectly lost: 0 bytes in 0 blocks
==66911== possibly lost: 0 bytes in 0 blocks
==66911== still reachable: 0 bytes in 0 blocks
==66911== suppressed: 0 bytes in 0 blocks
==66911==
==66911== For lists of detected and suppressed errors, rerun with: -s
==66911== ERROR SUMMARY: 1 errors from 1 contexts (suppressed: 0 from 0)
5.
- 实验代码，直接运行没有反应
#include <sys/types.h>
#include <unistd.h>
#include <iostream>
using namespace std;
int main()
{
int *data = (int *)malloc(100 * sizeof(int));
data[100] = 0;
return 0;
}
- valgrind输出两个错误
==67033== Memcheck, a memory error detector
==67033== Copyright (C) 2002-2017, and GNU GPL'd, by Julian Seward et al.
==67033== Using Valgrind-3.15.0 and LibVEX; rerun with -h for copyright info
==67033== Command: ./code5
==67033==
==67033== Invalid write of size 4
==67033== at 0x1091AD: main (code5.cpp:8)
==67033== Address 0x4da6e10 is 0 bytes after a block of size 400 alloc'd
==67033== at 0x483B7F3: malloc (in /usr/lib/x86_64-linux-gnu/valgrind/vgpreload_memcheck-amd64-linux.so)
==67033== by 0x10919E: main (code5.cpp:7)
==67033==
==67033==
==67033== HEAP SUMMARY:
==67033== in use at exit: 400 bytes in 1 blocks
==67033== total heap usage: 2 allocs, 1 frees, 73,104 bytes allocated
==67033==
==67033== 400 bytes in 1 blocks are definitely lost in loss record 1 of 1
==67033== at 0x483B7F3: malloc (in /usr/lib/x86_64-linux-gnu/valgrind/vgpreload_memcheck-amd64-linux.so)
==67033== by 0x10919E: main (code5.cpp:7)
==67033==
==67033== LEAK SUMMARY:
==67033== definitely lost: 400 bytes in 1 blocks
==67033== indirectly lost: 0 bytes in 0 blocks
==67033== possibly lost: 0 bytes in 0 blocks
==67033== still reachable: 0 bytes in 0 blocks
==67033== suppressed: 0 bytes in 0 blocks
==67033==
==67033== For lists of detected and suppressed errors, rerun with: -s
==67033== ERROR SUMMARY: 2 errors from 2 contexts (suppressed: 0 from 0)
6.
- 实验代码
#include <sys/types.h>
#include <unistd.h>
#include <iostream>
using namespace std;
int main()
{
int *data = (int *)malloc(100 * sizeof(int));
free(data);
cout << data[0];
return 0;
}
- valgrind输出
==67117== Memcheck, a memory error detector
==67117== Copyright (C) 2002-2017, and GNU GPL'd, by Julian Seward et al.
==67117== Using Valgrind-3.15.0 and LibVEX; rerun with -h for copyright info
==67117== Command: ./code6
==67117==
==67117== Invalid read of size 4
==67117== at 0x1091F3: main (code6.cpp:9)
==67117== Address 0x4da6c80 is 0 bytes inside a block of size 400 free'd
==67117== at 0x483CA3F: free (in /usr/lib/x86_64-linux-gnu/valgrind/vgpreload_memcheck-amd64-linux.so)
==67117== by 0x1091EE: main (code6.cpp:8)
==67117== Block was alloc'd at
==67117== at 0x483B7F3: malloc (in /usr/lib/x86_64-linux-gnu/valgrind/vgpreload_memcheck-amd64-linux.so)
==67117== by 0x1091DE: main (code6.cpp:7)
==67117==
==67117==
==67117== HEAP SUMMARY:
==67117== in use at exit: 0 bytes in 0 blocks
==67117== total heap usage: 3 allocs, 3 frees, 74,128 bytes allocated
==67117==
==67117== All heap blocks were freed -- no leaks are possible
==67117==
==67117== For lists of detected and suppressed errors, rerun with: -s
==67117== ERROR SUMMARY: 1 errors from 1 contexts (suppressed: 0 from 0)
7.
- 实验代码
#include <sys/types.h>
#include <unistd.h>
#include <iostream>
using namespace std;
int main()
{
int *data = (int *)malloc(100 * sizeof(int));
free(data + 10);
return 0;
}
- 运行结果,这次不用调试工具了
free(): invalid pointer
Aborted (core dumped)
8.
- 实验代码
#include <sys/types.h>
#include <unistd.h>
#include <iostream>
using namespace std;
int main()
{
int *data = (int *)malloc(2 * sizeof(int));
data = (int *)realloc(data, 11 * sizeof(int));
data[10] = 100;
free(data);
return 0;
}
- valgrind输出，没有报错
==67384== Memcheck, a memory error detector
==67384== Copyright (C) 2002-2017, and GNU GPL'd, by Julian Seward et al.
==67384== Using Valgrind-3.15.0 and LibVEX; rerun with -h for copyright info
==67384== Command: ./code8
==67384==
==67384==
==67384== HEAP SUMMARY:
==67384== in use at exit: 0 bytes in 0 blocks
==67384== total heap usage: 3 allocs, 3 frees, 72,756 bytes allocated
==67384==
==67384== All heap blocks were freed -- no leaks are possible
==67384==
==67384== For lists of detected and suppressed errors, rerun with: -s
==67384== ERROR SUMMARY: 0 errors from 0 contexts (suppressed: 0 from 0)
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