Question

我是C的新手，我正在和Valgrind一起练习。

我的代码：

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

int main()
{
    int i;
    int ints[10];
    char myString[50]; 

    for (i=0; i<=10; i++) {
        ints[i] = rand() % 10;
    }

    printf("''string'' is %lu characters long\n", strlen(myString));
    strcpy(myString, "This is a medium sized string");
    printf("''string'' is %lu characters long\n", strlen(myString));

    return 0;
}

我的Valgrind输出：

==5425== Syscall param write(buf) points to uninitialised byte(s)
==5425==    at 0x260E9A: write$NOCANCEL (in /usr/lib/system/libsystem_kernel.dylib)
==5425==    by 0x17E5E8: __sflush (in /usr/lib/system/libsystem_c.dylib)
==5425==    by 0x180CAA: __sfvwrite (in /usr/lib/system/libsystem_c.dylib)
==5425==    by 0x18B191: __vfprintf (in /usr/lib/system/libsystem_c.dylib)
==5425==    by 0x1AF2DA: __v2printf (in /usr/lib/system/libsystem_c.dylib)
==5425==    by 0x1AF6AF: __xvprintf (in /usr/lib/system/libsystem_c.dylib)
==5425==    by 0x186B29: vfprintf_l (in /usr/lib/system/libsystem_c.dylib)
==5425==    by 0x18496F: printf (in /usr/lib/system/libsystem_c.dylib)
==5425==    by 0x100000E73: main (test.c:15)
==5425==  Address 0x10001236e is 14 bytes inside a block of size 4,096 alloc'd
==5425==    at 0x6DEB: malloc (in /usr/local/Cellar/valgrind/3.9.0/lib/valgrind/vgpreload_memcheck-amd64-darwin.so)
==5425==    by 0x181855: __smakebuf (in /usr/lib/system/libsystem_c.dylib)
==5425==    by 0x196217: __swsetup (in /usr/lib/system/libsystem_c.dylib)
==5425==    by 0x1AF158: __v2printf (in /usr/lib/system/libsystem_c.dylib)
==5425==    by 0x1AF6AF: __xvprintf (in /usr/lib/system/libsystem_c.dylib)
==5425==    by 0x186B29: vfprintf_l (in /usr/lib/system/libsystem_c.dylib)
==5425==    by 0x18496F: printf (in /usr/lib/system/libsystem_c.dylib)
==5425==    by 0x100000E73: main (test.c:15)
==5425==  Uninitialised value was created by a stack allocation
==5425==    at 0x100000DF0: main (test.c:6)

我认为错误是由于当我进行第一次myString调用时printf为“空”这一事实，但是，我不确定如何解决它。< / p>

谢谢！

Answer 1

在此处调用myString时，字符strlen未初始化：

printf("''string'' is %lu characters long\n", strlen(myString));

当strlen函数通过myString搜索'\0'时，它会读取未初始化的数据。这就是在valgrind中触发错误的原因。

要解决此问题，请添加初始化：

char myString[50] = {0};

Answer 2

我认为错误是由于myString是＆＃34;空＆＃34;

不是真的。 myString不是空的，它未初始化，其内容未定义，因此使用strlen(myString)是非法的。

您可以将其初始化为空字符串，如下所示：

char myString[50] = "";

Answer 3

说myString为空，它有一些内容是不正确的。只是内容是任意的。

这意味着它可能不在那里的某个地方有一个零字节来终止字符串，所以在它上面调用printf或strlen是而不是一个好主意，因为它可能会在缓冲区的末尾运行并导致问题。

您可以通过确保它是一个有效的字符串来使其工作，例如：

*myString = '\0';

Valgrind中未初始化的字节错误

3 个答案: