C++例程摘录

读取配置文件

#include <iostream>
#include <fstream>
#include <sstream>
#include <cstdlib>
#include <string>
using namespace std;

int main()
{

    char    buf[1024];
    ifstream fin("../default.cfg");
    if (!fin.is_open()) {
        cerr << "open config file error\n";
        exit(1);
    }

    while (fin.getline(buf, 256)) {
        if (buf[0] == '#')         // drop the comment line

            continue;
        stringstream ss;
        ss << buf;
        string key, equal_token, value;
        ss >> key >> equal_token >> value;
        cout << "key = " << key << endl
            << "equal_token = " << equal_token << endl
            << "value = " << value << endl;
    }

    fin.close();
    return 0;
}

配置文件：

# drving style
DRIVING_STYLE    =     RA

对于更复杂的配置文件读取可用libconfig库

错误时输出当前文件，行号和函数

#include <iostream>
using namespace std;

#define WARNING(msg)    {cout << __FILE__ << " line" << __LINE__ \
                            << " " << __PRETTY_FUNCTION__ \
                            << ":" << msg << endl;}
int main()
{
    WARNING("connection failed");
    return 0;
}

数组初始化

int a[] = {1,2}; // ok

int *a = {1, 2}; // error

判断浮点数是否相等

#include <limits>
#include <cmath>
bool doubleCmp(double a, double b)
{
    return abs(a - b) < numeric_limits<double>::epsilon();
}

heap
改变<操作符定义前插入的元素大小顺序并不会因此改变

1,2范数计算

#include <limits>
#include <iostream>
#include <cmath>
#include <numeric>
using namespace std;

int norm1_add(double x, double y)
{
    return abs(x) + abs(y);
}
int norm2_add(double x, double y)
{
    return x + y * y;
}

int main()
{
    double a[] = {1, -2, 3};
    cout << accumulate(a, a + 3, 0, norm1_add) << endl;
    cout << accumulate(a, a + 3, 0, norm2_add) << endl;
    return 0;
}