char数组构造string

标签：c char c++ string

这是一个老掉牙的话题, 但是你稍加不注意就会出错.

最近在写一个可以跨平台打印的程序,就遇到这个问题,故记之.共勉!

用 char 数组初始化string

#include <string>

using std::string;
using std::cout;

int main(int argc, const char * argv[])
{
    char chArray[] = {'m', 'a', 'r', 'k'};
    cout << "array size = " << sizeof(chArray)/sizeof(char) << endl;
    cout << chArray << endl;
    string str(chArray);
    cout << "str = " << str << " and str's size = " << str.length() << endl;
}

在 mac 平台下,输出结果

array size = 4
mark\310\367\277_\377
str = mark\310\367\277_\377 and str's size = 10

但是有时候输出结果又是这样的

array size = 4
mark
str = mark and str's size = 5

思考一下,原来是少了 ‘\0‘, 修改上面代码

#include <string>

using std::string;
using std::cout;

int main(int argc, const char * argv[])
{
    char chArray[] = {'m', 'a', 'r', 'k', '\0'};
    cout << "array size = " << sizeof(chArray)/sizeof(char) << endl;
    cout << chArray << endl;
    string str(chArray);
    cout << "str = " << str << " and str's size = " << str.length() << endl;
}

array size = 5
mark
str = mark and str's size = 4

另外,要注意, string 的 size 要比 char 数组 size 小.

不知道上面的东西,你有没有看明白?

那么下面的代码输出,你觉得会达到自己的预期吗?

    const char * cp = str.c_str();
    unsigned long size = str.length();
    char chArray2[size];
    for (int i=0; i<size; i++) {
        chArray2[i] = cp[i];
        cout << chArray2[i] << endl;
    }
    
    string str2(chArray2);
    cout << "str2 = " << str2 << " and str2's size = " << str2.length() << endl;

ok, 这里很显然是错误的,至少两处是不对的.

1. chArray2的大小

2. chArray2的结束符没有添加 ‘\0‘

修改一下, 给出完整示例

#include <string>

using std::string;
using std::cout;

int main(int argc, const char * argv[])
{
    // char[] ---> string
    char chArray[] = {'m', 'a', 'r', 'k', '\0'};
    cout << "array size = " << sizeof(chArray)/sizeof(char) << endl;
    cout << chArray << endl;
    string str(chArray);
    cout << "str = " << str << " and str's size = " << str.length() << endl;
    
    // string --> char[]
    const char * cp = str.c_str();
    unsigned long size = str.length();
    char chArray2[size + 1];
    for (int i=0; i<size; i++) {
        chArray2[i] = cp[i];
        cout << chArray2[i] << endl;
    }
    chArray2[size] = '\0';
    
    string str2(chArray2);
    cout << "str2 = " << str2 << " and str2's size = " << str2.length() << endl;
}

的确,是这样,但是有时候需要 char 数组来操作,我也是把自己遇到的问题,加以总结跟大家分享一下.

把示例代码中的

char chArray[] = {'m', 'a', 'r', 'k', '\0'};

char chArray[] = "mark";

const char *chArray = "mark";

char数组构造string

标签：c char c++ string

原文地址：http://blog.csdn.net/veryitman/article/details/45402587