一些思考

非零即为真与返回值

链接出错的情况很多，可以表示非零表示，0是很唯一的一个数，成功也是只有一种情况，所以和0关联起来了。

返回值用int，那就是0表示成功返回值用bool，那就是true表示成功

// true 1
// false 0

// 返回值0一般表示true，other表示false

void test() {
  if (strcmp("aaa", "bbb")) {
    printf("same\n");
  } else {
    printf("not same\n");
  }

  if (strcmp("aaa", "bbb") == 0) {
    printf("same\n");
  } else {
    printf("not same\n");
  }
}

防御式编程与契约式编程

这种思想可以用来优化这个代码。下一节的do while0也可以。

// 如何防止出现
void fun1(int a, int b, int c) {
  if (a > 0) {
    if (b > 0) {
      if (c > 0) {
        printf("do something\n");
      }
    }
  }
}

// 可以这么写
void fun2(int a, int b, int c) {
  if (a <= 0) {
    return;
  }
  if (b <= 0) {
    return;
  }
  if (c <= 0) {
    return;
  }
  printf("do something\n");
}

推箱子的思考

小时候不会玩，现在依旧不会玩，推箱子的本质是什么

从推箱子领悟到了什么

do while（0）

可以代替goto

void fun1(int a, int b, int c) {
  char *mem = (char *)malloc(100);

  if (a > 0) {
    if (b > 0) {
      if (c > 0) {
        mem[0] = 10;
        printf("do something\n");
      }
    }
  }

  free(mem);
}

void fun2(int a, int b, int c) {
  char *mem = (char *)malloc(100);
  int ret = 0;
  do {
    if (a <= 0) {
      ret = -1;
      break;
    }
    if (b <= 0) {
      ret = -1;
      break;
    }
    if (c <= 0) {
      ret = -1;
      break;
    }
  } while(0);

  if (ret == 0) {
    mem[0] = 10;
    printf("do something\n");
    free(mem);
  }
}

字符创匹配的感受

思维方式的改变

int find_sub_str(const char *str, const char *substr) {
  for (int i = 0; str[i] != '\0'; i++) {
    int j = 0;
    for (j = 0; substr[j] != '\0'; j++) {
      if (str[i+j] != substr[j]) {
        break;
      }
    }
    if (substr[j] == '\0') {
      return i;
    }
  }
  return -1;
}


int find_sub_str_2(const char *str, const char *substr) {
  int i = 0; 
  int j = 0;
  while (str[i] != '\0' && substr[j] != '\0') {
    if (str[i] == substr[j]) {
            i++;
            j++;
    } else {
      i = i - j + 1;
      j = 0;
        }

    if (substr[j] == '\0') {
      return i - j;
    }
        // printf("i = %d, j = %d\n", i, j);
  }
  return -1;
}

yolo安装过程的思考

pkg-config，linux的这套机制懂了，编译出了问题才知道怎么解释
OpenCV mat和IplImage的不兼容，OpenCV1.x、2.x与OpenCV3.x以及以上

下列代码为什么会报错

namespace NAMEA {

class A {
public:
    virtual ~A();

    virtual int Init(const char* config_file) {
        return 0;
    }   
};
}

namespace NAMEB {

class NAMEA : public A {
 public:
  virtual ~NAMEA() {}
  int Init(const char* config_file) override {
    return 0;
  }
};

}

/*
$ g++ test.cpp
test.cpp:190:7: error: ‘int NAMEB::NAMEA::Init(const char*)’ marked ‘override’, but does not override
   int Init(const char* config_file) override {
       ^~~~
test.cpp: In function ‘void test_ptr(char**)’:
test.cpp:208:41: warning: format ‘%x’ expects argument of type ‘unsigned int’, but argument 2 has type ‘char*’ [-Wformat=]
  printf("in test_ptr ptr = 0x%x\n", *ptr);
                                     ~~~~^
test.cpp: In function ‘int main()’:
test.cpp:330:36: warning: format ‘%x’ expects argument of type ‘unsigned int’, but argument 2 has type ‘char*’ [-Wformat=]
  printf("in main ptr = 0x%x\n", ptr);
*/

左闭右开原则

链接

int array[10] = { 0 };
for (int i = 0; i < 10; i++) {
  array[i] = 100;
}

五子棋的设计

走一步分析一步与全局分析

递归的应用

打印字符串与求和

#include <iostream>
#include <cstring>

int sum(int *arr, int n) {
    //return n == 0 ? arr[0] : arr[n] + sum(arr, n-1);
    if (n == 0) {
        return arr[0];
    }
    return arr[n] + sum(arr, n-1);
}

int print_str_reverse(const char *str, int n) {
    if (n == 0) {
        printf("%c\n", str[0]);
        return 0;
    }
    printf("%c", str[n]);
    return print_str_reverse(str, n - 1);
}

int print_str(const char *str, int n = 0) {
    if (str[n] == '\0') {
        printf("\n");
        return 0;
    }
    printf("%c", str[n]);
    return print_str(str, n + 1);
}

int main()
{
    int arr[10] = {0, 1, 2, 3, 4, 5, 6, 7, 8, 9};
    int ret = sum(arr, 9);
    std::cout << "ret = " << ret << std::endl;

    print_str("0123456789");
    print_str_reverse("0123456789", strlen("0123456789") - 1);
    return 0;
}

#include <iostream>

class ISubject {
public:
  virtual void Request() = 0;
};

class RealSubject: public ISubject {
public:
  virtual void Request() {
    std::cout << "RealSubject::Request" << std::endl;
  }
};

class ProxySubject: public ISubject {
public:
  ProxySubject(ISubject *subject): subject_(subject) {}
  virtual void Request() {
    std::cout << "ProxySubject::Request" << std::endl;
    subject_->Request();
  }
private:
  ISubject *subject_;
};

class ProxySubject2: public ISubject {
public:
  ProxySubject2(): subject_(nullptr) {}
  virtual void Request() {
    if (!subject_) {
      subject_ = new RealSubject();
    }
    std::cout << "ProxySubject2::Request" << std::endl;
    subject_->Request();
  }
private:
  ISubject *subject_;
};

int main() {
  ISubject *subject = new RealSubject();
  ProxySubject *proxy_subject = new ProxySubject(subject);
  proxy_subject->Request();

  ProxySubject2 *proxy_subject2 = new ProxySubject2();
  proxy_subject2->Request();


  delete subject;
  delete proxy_subject;
  return 0;
}