1. 二级指针
int main() {
int (*p)[3];
int arr[2][3] = {{3,2,1},{4,5,6}};
// int arr[3] = {1,2,3};
// for (int i = 0; i < 3; ++i) {
// p[i] = arr;
// }
p = arr;
// int arr2[] = {4,5,6};
// p[1] = arr2;
printf("%d",**p);
printf("%d",*(*p+1));
printf("%d",*(*p+2));
printf("%d",*(*(p+1)+1));
printf("%d",*(p[1]+2));
for (int i = 0; i < 2; ++i) {
printf("\nindex %d\n",i);
for (int j = 0; j < 3; ++j) {
// printf("arr %d ",*(*(p+i)+j));
printf("arr %d ",(*(p+i))[j]);
}
}
return 0;
}
2.结构体
//结构体使用 People与Student区别 People是一个全局变量 Student是一个结构体类型
struct _People{
char* name;
int age;
}People;
typedef _People ZZ;
typedef struct _Student{
char* name;
int age;
}Student;
int main() {
// ZZ a;
// struct _People a{"zz",12};
// a.age = 25;
// a.name = "dabaicai";
// printf("a name is %s age is %d",a.name,a.age);
// People.name = "dabaicai";
// People.age = 25;
// printf("People name is %s age is %d",People.name,People.age);
// struct _Student ss{"aa",12};
Student ss;
ss.name = "dabaicai";
ss.age = 25;
printf("ss name is %s age is %d",ss.name,ss.age);
return 0;
}
3.类
-----------------------------------h----------------------------------------------
#ifndef UNTITLED_STUDENT_H
#define UNTITLED_STUDENT_H
class Student {
private:
static Student *instance;
Student();
int age;
public:
char *name;
Student(int age);
static Student *getInstance();
void friend setAge(Student *student);
Student operator+(const Student &student) {
Student temp;
temp.age = this->age + student.age;
return temp;
};
int getAge(){
return age;
}
};
#endif //UNTITLED_STUDENT_H
-----------------------------------cpp----------------------------------------------
Student* Student::instance = 0;
Student*Student::getInstance() {
if(!instance){
instance = new Student();
}
return instance;
}
Student::Student() {
}
Student::Student(int age) {
this->age = age;
}
-----------------------------------main---------------------------------------------
#include <iostream>
#include "Student.h"
//友元函数
void setAge(Student * student){
student->age = 25;
}
int main() {
Student* student = Student::getInstance();
setAge(student);
Student* student2 = new Student(50);
Student student1 = *student + *student2;
printf("student age is %d",student1.getAge());
return 0;
}
4.模板
#include <iostream>
template<class T, class E>
class Q {
public:
T test(T t, E e) {
return t + e;
}
};
template<class T>
T zz(T a, T b) {
return a + b;
}
int main() {
Q<int, float> q;
std::cout << q.test(1, 1.5f) << std::endl;
std::cout << zz(1, 4);
return 0;
}
5.命名空间
可以区分二个同名函数
#include <iostream>
template<class T, class E>
class Q {
public:
T test(T t, E e) {
return t + e;
}
};
int add(int a, int b) {
return a + b;
}
float add(float a, float b) {
return a + b;
}
template<class T>
T zz(T a, T b) {
return a + b;
}
namespace first_space{
void func(){
printf("first space func");
}
}
namespace second_space{
void func(){
printf("second space func");
}
}
int main() {
first_space::func();
second_space::func();
int i = 1;
int&b = i;
int c = i;
printf("\ni is %d,&b is %d,c is %d",&i,&b,&c);
//i is -274684040,&b is -274684040,c is -274684052
return 0;
}
6.gcc编译四步骤
1.预处理（ Pre-Processing ）：将要包含(include)的文件插入原文件中、将宏定义展开、根据条件编译命令选择要使用的代码
gcc -E -o add.i add.c
2.编译（ Compiling ）：检查代码规范，错误等后将代码翻译成汇编代码
gcc -S -o add.s add.i
3.汇编（ Assembling ）：生成目标文件.o文件，将汇编代码生成目标(机器)代码
gcc -c add.cpp -o add.o (最耗时)
4.链接（ Linking ）：将汇编生成的OBJ文件、系统库的OBJ文件、库文件链接起来，最终生成可以在特定平台运行的可执行程(文件)
gcc add.o -o add (生成可执行文件add)
7.生成静态库
ar 将目标文件打包成静态库
ar t xxx.a 查看静态库内容
//add.h
int add(int a,int b);
//add.c
#include "add.h"
int add(int a,int b){
return a+b;
}
//main.c
#include<stdio.h>
#include "add.h"
int main(){
int a = add(1,2);
printf("a = %d",a);
return 0;
}
1. gcc -c add.c //将 add.c 编译成 add.o
2. ar rcs libadd.a add.o //将 add.o 生成静态库文件
3. gcc -o main main.c -L. -ladd // 将 main.c 编译并链接 libadd.a 库文件
---------------------------------------------
执行 ./main
输出 a = 3
8.生成动态库
1. gcc -c add.c //将 add.c 编译成 add.o
2.gcc -shared -fPIC -o libadd.so add.o //生成动态库
3.gcc -o main main.c -L. -ladd // 将 main.c 编译并链接 libadd.so 库文件
---------------------------------------------
linux下执行 LD_LIBRARY_PATH=. ./main
mac下执行 ./main
输出 a = 3
---------------------------------------------
linux 执行 ldd main
linux-vdso.so.1 => (0x00007ffe8aeb9000)
libtool.so => not found
libc.so.6 => /lib64/libc.so.6 (0x00007f2c0c74b000)
/lib64/ld-linux-x86-64.so.2 (0x0000555dd56da000)
注意：在linux上直接执行 ./main 会报 ./main: error while loading shared libraries: libtool.so: cannot open shared object file: No such file or directory 这个错误 ，原因是生成的动态库在默认查找的动态库目录下没有(可以用 ldd main 查看查找动态库目录)，所以要设置查找目录。
而在 mac 下直接执行不会报，目前不清楚。。
