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全部学习汇总： GreyZhang/c_basic: little bits of c. (github.com) 欢迎路过的YUAN类朋友相互沟通交流，也欢迎各位随时指点指正。以下是我的联系方式： C语言是我现在吃饭的家伙，但是我的家伙事儿确实是维护保养的不够好。很多细枝末节的东西没有学习到位，虽说日常工作中还没遇到多少问题，不过与同行打交道的时候遇到的问题着实不少。 刚刚工作的时候，遇到了一次局部变量没有初始化结果出现非预期结果的问题。离职之后尝试面试的时候，一个面试题问我使用什么函数可以把变量初值初始化为0，我也蒙了。我工作中，全局变量的初始化初值默认一直是0啊！其实，这个问题我到现在还不知道答案，根本没有对此进行深究学习。不过，从面试官那里得到的答案是这个跟编译器等多个因素是有关系的。 今晚在翻一本C语言的经典教程数目，再次看到了局部变量初始化的问题。不过书中没有指明编译器，也没有说明是否全局变量亦是如此。我手头暂时只有gcc，决定用gcc编译器做一个简单的测试，测试手段使用Python。通过重复变异执行，搜集全局量与局部量的10组结果。 局部变量初始化测试编写代码如下：
全局变量初始化测试编写代码如下：
测试脚本编写如下：
测试的数据结果如下： 局部变量测试： Test for 1 times: Compiling... executing... array_num[0] = 1 array_num[1] = 0 array_num[2] = 4203625 array_num[3] = 0 array_num[4] = 3 array_num[5] = 0 array_num[6] = 6 array_num[7] = 0 array_num[8] = 0 array_num[9] = 0 Test for 2 times: Compiling... executing... array_num[0] = 1 array_num[1] = 0 array_num[2] = 4203625 array_num[3] = 0 array_num[4] = 3 array_num[5] = 0 array_num[6] = 6 array_num[7] = 0 array_num[8] = 0 array_num[9] = 0 Test for 3 times: Compiling... executing... array_num[0] = 1 array_num[1] = 0 array_num[2] = 4203625 array_num[3] = 0 array_num[4] = 3 array_num[5] = 0 array_num[6] = 6 array_num[7] = 0 array_num[8] = 0 array_num[9] = 0 Test for 4 times: Compiling... executing... array_num[0] = 1 array_num[1] = 0 array_num[2] = 4203625 array_num[3] = 0 array_num[4] = 3 array_num[5] = 0 array_num[6] = 6 array_num[7] = 0 array_num[8] = 0 array_num[9] = 0 Test for 5 times: Compiling... executing... array_num[0] = 1 array_num[1] = 0 array_num[2] = 4203625 array_num[3] = 0 array_num[4] = 3 array_num[5] = 0 array_num[6] = 6 array_num[7] = 0 array_num[8] = 0 array_num[9] = 0 Test for 6 times: Compiling... executing... array_num[0] = 1 array_num[1] = 0 array_num[2] = 4203625 array_num[3] = 0 array_num[4] = 3 array_num[5] = 0 array_num[6] = 6 array_num[7] = 0 array_num[8] = 0 array_num[9] = 0 Test for 7 times: Compiling... executing... array_num[0] = 1 array_num[1] = 0 array_num[2] = 4203625 array_num[3] = 0 array_num[4] = 3 array_num[5] = 0 array_num[6] = 6 array_num[7] = 0 array_num[8] = 0 array_num[9] = 0 Test for 8 times: Compiling... executing... array_num[0] = 1 array_num[1] = 0 array_num[2] = 4203625 array_num[3] = 0 array_num[4] = 3 array_num[5] = 0 array_num[6] = 6 array_num[7] = 0 array_num[8] = 0 array_num[9] = 0 Test for 9 times: Compiling... executing... array_num[0] = 1 array_num[1] = 0 array_num[2] = 4203625 array_num[3] = 0 array_num[4] = 3 array_num[5] = 0 array_num[6] = 6 array_num[7] = 0 array_num[8] = 0 array_num[9] = 0 Test for 10 times: Compiling... executing... array_num[0] = 1 array_num[1] = 0 array_num[2] = 4203625 array_num[3] = 0 array_num[4] = 3 array_num[5] = 0 array_num[6] = 6 array_num[7] = 0 array_num[8] = 0 array_num[9] = 0 全局变量初始化测试： Test for 1 times: Compiling... executing... array_num[0] = 0 array_num[1] = 0 array_num[2] = 0 array_num[3] = 0 array_num[4] = 0 array_num[5] = 0 array_num[6] = 0 array_num[7] = 0 array_num[8] = 0 array_num[9] = 0 Test for 2 times: Compiling... executing... array_num[0] = 0 array_num[1] = 0 array_num[2] = 0 array_num[3] = 0 array_num[4] = 0 array_num[5] = 0 array_num[6] = 0 array_num[7] = 0 array_num[8] = 0 array_num[9] = 0 Test for 3 times: Compiling... executing... array_num[0] = 0 array_num[1] = 0 array_num[2] = 0 array_num[3] = 0 array_num[4] = 0 array_num[5] = 0 array_num[6] = 0 array_num[7] = 0 array_num[8] = 0 array_num[9] = 0 Test for 4 times: Compiling... executing... array_num[0] = 0 array_num[1] = 0 array_num[2] = 0 array_num[3] = 0 array_num[4] = 0 array_num[5] = 0 array_num[6] = 0 array_num[7] = 0 array_num[8] = 0 array_num[9] = 0 Test for 5 times: Compiling... executing... array_num[0] = 0 array_num[1] = 0 array_num[2] = 0 array_num[3] = 0 array_num[4] = 0 array_num[5] = 0 array_num[6] = 0 array_num[7] = 0 array_num[8] = 0 array_num[9] = 0 Test for 6 times: Compiling... executing... array_num[0] = 0 array_num[1] = 0 array_num[2] = 0 array_num[3] = 0 array_num[4] = 0 array_num[5] = 0 array_num[6] = 0 array_num[7] = 0 array_num[8] = 0 array_num[9] = 0 Test for 7 times: Compiling... executing... array_num[0] = 0 array_num[1] = 0 array_num[2] = 0 array_num[3] = 0 array_num[4] = 0 array_num[5] = 0 array_num[6] = 0 array_num[7] = 0 array_num[8] = 0 array_num[9] = 0 Test for 8 times: Compiling... executing... array_num[0] = 0 array_num[1] = 0 array_num[2] = 0 array_num[3] = 0 array_num[4] = 0 array_num[5] = 0 array_num[6] = 0 array_num[7] = 0 array_num[8] = 0 array_num[9] = 0 Test for 9 times: Compiling... executing... array_num[0] = 0 array_num[1] = 0 array_num[2] = 0 array_num[3] = 0 array_num[4] = 0 array_num[5] = 0 array_num[6] = 0 array_num[7] = 0 array_num[8] = 0 array_num[9] = 0 Test for 10 times: Compiling... executing... array_num[0] = 0 array_num[1] = 0 array_num[2] = 0 array_num[3] = 0 array_num[4] = 0 array_num[5] = 0 array_num[6] = 0 array_num[7] = 0 array_num[8] = 0 array_num[9] = 0 从上面展示的这些数据来看，全局变量的定义默认初始化数值应该是0。至少，从gcc编译器来看的话应该是0。而局部变量的初始化应该是有非0数值，但是出现0的概率也是蛮高的，我手头的这本书中说的变量（没有指明是否是局部变量）的初始化数值是随机的。我尝试修改了代码的文件名，尝试修改了目录，测试的数据跟之前的数据完全一样。测试不够充分，但是大致能够给我一点实际的说明信息了。 附加一下我使用的软件版本： gcc 4.9.2，Python 2.7.6 |
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