这是1个老掉牙的话题,但是你略加不注意就会出错.
最近在写1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;
}
针对上面的代码,不同的编译器输出结果不1致,并且具有随机性.
在 mac 平台下,输出结果
array size = 4
mark310367277_377
str = mark310367277_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
很明显,string 的 size 不对.#include <string>
using std::string;
using std::cout;
int main(int argc,'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;
}
输出也正常了.
array size = 5
mark
str = mark and str's size = 4
也就是说,char 数组初始化 string 对象,数组的结束符 ' ' 不要忘记了.
另外,要注意,string 的 size 要比 char 数组 size 小.
不知道上面的东西,你有无看明白?
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,这里很明显是毛病的,最少两处是不对的.
1. chArray2的大小
2. chArray2的结束符没有添加 ' '
修改1下,给出完全示例
#include <string>
using std::string;
using std::cout;
int main(int argc,const char * argv[])
{
// char[] ---> string
char chArray[] = {'m',' '};
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] = ' ';
string str2(chArray2);
cout << "str2 = " << str2 << " and str2's size = " << str2.length() << endl;
}
或许有人会说,为何要用 char 数组去构造 string 对象,用 char *(指针)不是更好吗?
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1下.
把示例代码中的
char chArray[] = {'m',' '};
修改成
char chArray[] = "mark";
或
const char *chArray = "mark";
代码也能够正常正确的输出.
