C++ Valgrind正在报道；使用大小为4”的未初始化值；使用strlen时

我想在覆盆子皮上用Valgrind。我正在分析以下程序：

#include <string>
#include <cstring>

int main() {
    std::string blaat = "blaat";
    const char * buf = blaat.c_str();
    size_t l = 0;
    l = strlen(buf);
    printf("string size %u\n", l);
}

分析（valgrind-3.16.1）：

结果:

==29572==
==29572== Conditional jump or move depends on uninitialised value(s)
==29572==    at 0x4866210: ??? (in /usr/lib/arm-linux-gnueabihf/libarmmem-v7l.so)
==29572==
==29572== Conditional jump or move depends on uninitialised value(s)
==29572==    at 0x48662DC: ??? (in /usr/lib/arm-linux-gnueabihf/libarmmem-v7l.so)
==29572==
==29572== Use of uninitialised value of size 4
==29572==    at 0x4AABF6C: _itoa_word (_itoa.c:179)
==29572==    by 0x4AB0727: vfprintf (vfprintf.c:1637)
==29572==    by 0x4AB646F: printf (printf.c:33)
==29572==    by 0x1088F: main (test.c:10)
==29572==
==29572== Conditional jump or move depends on uninitialised value(s)
==29572==    at 0x4AABF74: _itoa_word (_itoa.c:179)
==29572==    by 0x4AB0727: vfprintf (vfprintf.c:1637)
==29572==    by 0x4AB646F: printf (printf.c:33)
==29572==    by 0x1088F: main (test.c:10)
==29572==
==29572== Conditional jump or move depends on uninitialised value(s)
==29572==    at 0x4AAF8FC: vfprintf (vfprintf.c:1637)
==29572==    by 0x4AB646F: printf (printf.c:33)
==29572==    by 0x1088F: main (test.c:10)
==29572==
==29572== Conditional jump or move depends on uninitialised value(s)
==29572==    at 0x4AAF99C: vfprintf (vfprintf.c:1637)
==29572==    by 0x4AB646F: printf (printf.c:33)
==29572==    by 0x1088F: main (test.c:10)
==29572==
==29572== Conditional jump or move depends on uninitialised value(s)
==29572==    at 0x4AAFA00: vfprintf (vfprintf.c:1637)
==29572==    by 0x4AB646F: printf (printf.c:33)
==29572==    by 0x1088F: main (test.c:10)
==29572==
==29572== Conditional jump or move depends on uninitialised value(s)
==29572==    at 0x4AAFA7C: vfprintf (vfprintf.c:1637)
==29572==    by 0x4AB646F: printf (printf.c:33)
==29572==    by 0x1088F: main (test.c:10)

---

一旦我使用“strlen”，Valgrind似乎会对未初始化的值发出警告。为什么？

如果您使用表示大小t的

%zu

，而不是表示无符号int的

%u

，这有关系吗？或者，

static\u cast（l）

。这两种选择都没有改变Valgrind的输出-仍然会收到警告如果你想让它们静音：这就是glibc在ARM上的工作方式，我一直都会收到这种错误。我认为这是出于性能原因。页面总是以4个字节的倍数对齐，因此通常一次检查4个字节以查找

strlen（）

。将valgrind抑制作为一种解决方法。strlen的输出用作sendbuffer（数据，sz）函数的参数。现在Valgrind还将报告此函数正在使用统一化字节。因此，我必须将sendbuffer添加到抑制文件中，而不是将strlen添加到抑制文件中。然而，这些函数是我想要检查的。

valgrind --leak-check=yes ./a.out

==29572==
==29572== Conditional jump or move depends on uninitialised value(s)
==29572==    at 0x4866210: ??? (in /usr/lib/arm-linux-gnueabihf/libarmmem-v7l.so)
==29572==
==29572== Conditional jump or move depends on uninitialised value(s)
==29572==    at 0x48662DC: ??? (in /usr/lib/arm-linux-gnueabihf/libarmmem-v7l.so)
==29572==
==29572== Use of uninitialised value of size 4
==29572==    at 0x4AABF6C: _itoa_word (_itoa.c:179)
==29572==    by 0x4AB0727: vfprintf (vfprintf.c:1637)
==29572==    by 0x4AB646F: printf (printf.c:33)
==29572==    by 0x1088F: main (test.c:10)
==29572==
==29572== Conditional jump or move depends on uninitialised value(s)
==29572==    at 0x4AABF74: _itoa_word (_itoa.c:179)
==29572==    by 0x4AB0727: vfprintf (vfprintf.c:1637)
==29572==    by 0x4AB646F: printf (printf.c:33)
==29572==    by 0x1088F: main (test.c:10)
==29572==
==29572== Conditional jump or move depends on uninitialised value(s)
==29572==    at 0x4AAF8FC: vfprintf (vfprintf.c:1637)
==29572==    by 0x4AB646F: printf (printf.c:33)
==29572==    by 0x1088F: main (test.c:10)
==29572==
==29572== Conditional jump or move depends on uninitialised value(s)
==29572==    at 0x4AAF99C: vfprintf (vfprintf.c:1637)
==29572==    by 0x4AB646F: printf (printf.c:33)
==29572==    by 0x1088F: main (test.c:10)
==29572==
==29572== Conditional jump or move depends on uninitialised value(s)
==29572==    at 0x4AAFA00: vfprintf (vfprintf.c:1637)
==29572==    by 0x4AB646F: printf (printf.c:33)
==29572==    by 0x1088F: main (test.c:10)
==29572==
==29572== Conditional jump or move depends on uninitialised value(s)
==29572==    at 0x4AAFA7C: vfprintf (vfprintf.c:1637)
==29572==    by 0x4AB646F: printf (printf.c:33)
==29572==    by 0x1088F: main (test.c:10)