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POMalloc, string pointers, and Valgrind
 

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  1. POMalloc, string pointers, and Valgrind
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    <p>My program is like this (<strong>main.c</strong>):</p> <pre><code>#include &lt;stdlib.h&gt; #include &lt;stdio.h&gt; void main(){ char *first="hello "; char *second="world!"; char *seq=(char *)malloc((strlen(first)+1)*sizeof(char)); strcat(strcpy(seq,first),second); printf("%s\n",seq); free(seq); } </code></pre> <p>and I debug with the tool valgrind, it said that($:valgrind --tool=memcheck --leak-check=full --track-origins=yes ./main):</p> <pre><code>==5118== Memcheck, a memory error detector. ==5118== Copyright (C) 2002-2008, and GNU GPL'd, by Julian Seward et al. ==5118== Using LibVEX rev 1884, a library for dynamic binary translation. ==5118== Copyright (C) 2004-2008, and GNU GPL'd, by OpenWorks LLP. ==5118== Using valgrind-3.4.1, a dynamic binary instrumentation framework. ==5118== Copyright (C) 2000-2008, and GNU GPL'd, by Julian Seward et al. ==5118== For more details, rerun with: -v ==5118== ==5118== Invalid write of size 1 ==5118== at 0x402575B: strcat (in /usr/lib/valgrind/x86-linux/vgpreload_memcheck.so) ==5118== by 0x80484EB: main (main.c:7) ==5118== Address 0x418a02f is 0 bytes after a block of size 7 alloc'd ==5118== at 0x402522D: malloc (in /usr/lib/valgrind/x86-linux/vgpreload_memcheck.so) ==5118== by 0x80484C3: main (main.c:6) ==5118== ==5118== Invalid write of size 1 ==5118== at 0x4025777: strcat (in /usr/lib/valgrind/x86-linux/vgpreload_memcheck.so) ==5118== by 0x80484EB: main (main.c:7) ==5118== Address 0x418a034 is 5 bytes after a block of size 7 alloc'd ==5118== at 0x402522D: malloc (in /usr/lib/valgrind/x86-linux/vgpreload_memcheck.so) ==5118== by 0x80484C3: main (main.c:6) ==5118== ==5118== Invalid read of size 1 ==5118== at 0x4025963: strlen (in /usr/lib/valgrind/x86-linux/vgpreload_memcheck.so) ==5118== by 0x40A0FA4: puts (in /lib/libc-2.10.1.so) ==5118== by 0x80484F7: main (main.c:8) ==5118== Address 0x418a02f is 0 bytes after a block of size 7 alloc'd ==5118== at 0x402522D: malloc (in /usr/lib/valgrind/x86-linux/vgpreload_memcheck.so) ==5118== by 0x80484C3: main (main.c:6) ==5118== ==5118== Invalid read of size 1 ==5118== at 0x40ACEFE: _IO_default_xsputn (in /lib/libc-2.10.1.so) ==5118== by 0x40AA3D0: _IO_file_xsputn@@GLIBC_2.1 (in /lib/libc-2.10.1.so) ==5118== by 0x40A1020: puts (in /lib/libc-2.10.1.so) ==5118== by 0x80484F7: main (main.c:8) ==5118== Address 0x418a02f is 0 bytes after a block of size 7 alloc'd ==5118== at 0x402522D: malloc (in /usr/lib/valgrind/x86-linux/vgpreload_memcheck.so) ==5118== by 0x80484C3: main (main.c:6) hello world! ==5118== ==5118== ERROR SUMMARY: 17 errors from 4 contexts (suppressed: 13 from 1) ==5118== malloc/free: in use at exit: 7 bytes in 1 blocks. ==5118== malloc/free: 1 allocs, 0 frees, 7 bytes allocated. ==5118== For counts of detected errors, rerun with: -v ==5118== searching for pointers to 1 not-freed blocks. ==5118== checked 47,492 bytes. ==5118== ==5118== ==5118== 7 bytes in 1 blocks are definitely lost in loss record 1 of 1 ==5118== at 0x402522D: malloc (in /usr/lib/valgrind/x86-linux/vgpreload_memcheck.so) ==5118== by 0x80484C3: main (main.c:6) ==5118== ==5118== LEAK SUMMARY: ==5118== definitely lost: 7 bytes in 1 blocks. ==5118== possibly lost: 0 bytes in 0 blocks. ==5118== still reachable: 0 bytes in 0 blocks. ==5118== suppressed: 0 bytes in 0 blocks. </code></pre> <p>Who can tell me why and how to fix it.</p>
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