一、若程序中存在迷途指针，轻则导致程序退出，重则使程序出现重大逻辑错误
1、定义：内存已释放，指针依旧指向原始内存，这种指针就是迷途指针
2、迷途指针和指针别名：
1）、指针依旧指向已释放的内存，无法访问内存中的内容；
2）、迷途指针没有指向有效对象，也称为内存过早释放；
3）、两个指针指向同一个内存区域，称为指针别名；
4）、使用指针别名的程序容易出现迷途指针，任意释放一个指针的内存即可，不需要每个都释放一下；
5）、linux中使用工具valgrind，使用命令valgrind --tool=memcheck --leak-check=yes fileName检测程序fileName的内存泄露情况；
3、代码形式：
1）、指针依旧指向已释放的内存，无法访问内存中的内容；
int *ptrInt1 = (int *)malloc(sizeof(int)); *ptrInt = 9;free(ptrInt1); …
*ptrInt1 = 10;
2）、迷途指针没有指向有效对象，也称为内存过早释放；
int *ptrInt1 = (int *)malloc(sizeof(int)); *ptrInt = 9; free(ptrInt1); …
printf("%d",*ptrInt1);
3）、两个指针指向同一个内存区域，称为指针别名；
int *ptrInt1 = (int *)malloc(sizeof(int)); *ptrInt = 9; … int *ptrInt2 = ptrInt1; … free(ptrInt1); … *ptrInt1 = 10;
4）、使用指针别名的程序容易出现迷途指针，任意释放一个指针的内存即可，不需要每个都释放一下；
int *ptrInt1 = (int *)malloc(sizeof(int)); *ptrInt = 9; … int *ptrInt2 = ptrInt1; … free(ptrInt1); … free(ptrInt2);
5）、linux中使用工具valgrind，使用命令valgrind --tool=memcheck --leak-check=yes fileName检测程序fileName的内存泄露情况；
1 #include <stdio.h> 2 #include <stdlib.h> 3 4 int main(int argc, char **argv) 5 { 6 int *ptrInt = (int *)malloc(sizeof(int) * 6); 7 int size = 6; 8 for(int i = 0; i < size; i++){ 9 *(ptrInt + i) = 90 + i; 10 } 11 12 for(int i = 0; i < size; i++){ 13 printf("ptrInt[%d]: %d ", i, *(ptrInt + i)); 14 } 15 free(ptrInt); 16 17 return 0; 18 }
将上述代码编译后生成test14可执行文件，使用命令：valgrind --tool=memcheck --leak-check=yes test14，结果为
develop � … � CodeStudy � cnblogs_understanding_and_using_c_pointers � chapter2 � valgrind --tool=memcheck --leak-check=yes test14 ==1513== Memcheck, a memory error detector ==1513== Copyright (C) 2002-2017, and GNU GPL'd, by Julian Seward et al. ==1513== Using Valgrind-3.13.0 and LibVEX; rerun with -h for copyright info ==1513== Command: test14 ==1513== ptrInt[0]: 90 ptrInt[1]: 91 ptrInt[2]: 92 ptrInt[3]: 93 ptrInt[4]: 94 ptrInt[5]: 95 ==1513== ==1513== HEAP SUMMARY: ==1513== in use at exit: 0 bytes in 0 blocks ==1513== total heap usage: 2 allocs, 2 frees, 1,048 bytes allocated ==1513== ==1513== All heap blocks were freed -- no leaks are possible ==1513== ==1513== For counts of detected and suppressed errors, rerun with: -v ==1513== ERROR SUMMARY: 0 errors from 0 contexts (suppressed: 0 from 0)
上述结果没有发生内存泄露，若将第15行代码注释掉，重新编译，执行命令：valgrind --tool=memcheck --leak-check=yes test14，结果为
cnblogs_understanding_and_using_c_pointers � chapter2 � valgrind --tool=memcheck --leak-check=yes test14 ==1908== Memcheck, a memory error detector ==1908== Copyright (C) 2002-2017, and GNU GPL'd, by Julian Seward et al. ==1908== Using Valgrind-3.13.0 and LibVEX; rerun with -h for copyright info ==1908== Command: test14 ==1908== ptrInt[0]: 90 ptrInt[1]: 91 ptrInt[2]: 92 ptrInt[3]: 93 ptrInt[4]: 94 ptrInt[5]: 95 ==1908== ==1908== HEAP SUMMARY: ==1908== in use at exit: 24 bytes in 1 blocks ==1908== total heap usage: 2 allocs, 1 frees, 1,048 bytes allocated ==1908== ==1908== 24 bytes in 1 blocks are definitely lost in loss record 1 of 1 ==1908== at 0x4C2CE5F: malloc (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so) ==1908== by 0x1086B2: main (test14.c:6) ==1908== ==1908== LEAK SUMMARY: ==1908== definitely lost: 24 bytes in 1 blocks ==1908== indirectly lost: 0 bytes in 0 blocks ==1908== possibly lost: 0 bytes in 0 blocks ==1908== still reachable: 0 bytes in 0 blocks ==1908== suppressed: 0 bytes in 0 blocks ==1908== ==1908== For counts of detected and suppressed errors, rerun with: -v ==1908== ERROR SUMMARY: 1 errors from 1 contexts (suppressed: 0 from 0)
检查表明有一处内存泄露，有24个字节内存泄露，其他的请参看valgrind的帮助文档，man valgrind即可，非常方便。