和前面的memcpy类似， strcpy/strncpy/strcat/strncat都存在内存重叠问题， 为了简便示意起见， 我用strcpy做例子来说明。 值得注意， 有时候， 在你的环境下， strcpy没有出现如下的问题， 不表明他真的没有问题。 看程序：
#include <stdio.h> #include <string.h> int main() { char str[100] = "abcdefghijklmn"; strncpy(str + 2, str, 5); printf("%s\n", str); return 0; }结果为：
[root@xxx ~/valgrind-3.8.1/bin]# g++ -g test.cpp [root@xxx ~/valgrind-3.8.1/bin]# ./a.out cdefgfghijklmn [root@xxx ~/valgrind-3.8.1/bin]#虽然暂时没有异常， 但这也仅仅是运气。 用 valgrind搞起：
[root@xxx ~/valgrind-3.8.1/bin]# g++ -g test.cpp [root@xxx ~/valgrind-3.8.1/bin]# [root@xxx ~/valgrind-3.8.1/bin]# ./valgrind --tool=memcheck --leak-check=yes --show-reachable=yes ./a.out ==318== Memcheck, a memory error detector ==318== Copyright (C) 2002-2012, and GNU GPL'd, by Julian Seward et al. ==318== Using Valgrind-3.8.1 and LibVEX; rerun with -h for copyright info ==318== Command: ./a.out ==318== ==318== Source and destination overlap in strncpy(0x7ff000475, 0x7ff000477, 5) ==318== at 0x4C290FF: strncpy (mc_replace_strmem.c:472) ==318== by 0x400640: main (test.cpp:7) ==318== cdefgfghijklmn ==318== ==318== HEAP SUMMARY: ==318== in use at exit: 0 bytes in 0 blocks ==318== total heap usage: 0 allocs, 0 frees, 0 bytes allocated ==318== ==318== All heap blocks were freed -- no leaks are possible ==318== ==318== For counts of detected and suppressed errors, rerun with: -v ==318== ERROR SUMMARY: 1 errors from 1 contexts (suppressed: 6 from 6) [root@xxx ~/valgrind-3.8.1/bin]# 可见， valgrind是提示了错误的。
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