C++ 整數轉字串
阿新 • • 發佈:2021-01-21
在寫程式碼時,偶然把一個char型加上‘\0‘,結果發現其實加不加都無所謂,int都能轉string型。比如:
int c=48;
string s0,s1;
for (int i=0;i<10;i++){
s0=c+i;
s1=c+i+'0'; //+'0'等價於+48
cout<<c+i+'\0'<<"~"<<s0<<"~"<<s1<<endl;
}
顯示結果:
48~0~`
49~1~a
50~2~b
51~3~c
52~4~d
53~5~e
55~7~g
56~8~h
57~9~i
--------------------------------
結論:整數與256的餘數就是它轉字串的那個字母的ascii碼。
現在把任意整數各位上的0~9分別轉字元,就能實現整數轉字串itoString()了:
#include <iostream> #include <string> #include <climits> using namespace std; string itoString(int i) { int n; string s,t; if (i==INT_MIN) return itoString(INT_MIN/10)+itoString(-(INT_MIN%10)); n=i>0?i:-i; do{ t=(char)(n%10+48)+'\0'; s=t+s; n=n/10; } while(n>0); return i>0?s:"-"+s; } string ltoString(long int i) { long int n; string s,t; if (i==LONG_MIN) return ltoString(LONG_MIN/10)+ltoString(-(LONG_MIN%10)); n=i>0?i:-i; do{ t=(char)(n%10+48)+'\0'; s=t+s; n=n/10; } while(n>0); return i>0?s:"-"+s; } string lltoString(long long i) { long long n; string s,t; if (i==LONG_LONG_MIN) return lltoString(LONG_LONG_MIN/10)+lltoString(-(LONG_LONG_MIN%10)); n=i>0?i:-i; do{ t=(char)(n%10+48)+'\0'; s=t+s; n=n/10; } while(n>0); return i>0?s:"-"+s; } int main(void) { int i; long long j; cout<<"整數轉字串測試:"<<endl; for (i=-10;i<=10;i++) cout<<itoString(i)<<" "; cout<<endl<<endl; i=1234567890; cout<<i<<"轉字串:"<<itoString(i)<<endl; cout<<-i/10<<"轉字串:"<<itoString(-i/10)<<endl<<endl; j=8976543210123456789; cout<<j<<"轉字串:"<<lltoString(j)<<endl; cout<<-j/10<<"轉字串:"<<lltoString(-j/10)<<endl<<endl; cout<<"int型的數值範圍是:"<<itoString(INT_MIN)<<","<<itoString(INT_MAX)<<endl; cout<<"long int型的數值範圍:"<<ltoString(LONG_MIN)<<","<<ltoString(LONG_MAX)<<endl; cout<<"long long型的數值範圍:"<<lltoString(LONG_LONG_MIN)<<","<<lltoString(LONG_LONG_MAX)<<endl; return 0; }
測試結果:
整數轉字串測試: -10 -9 -8 -7 -6 -5 -4 -3 -2 -1 -0 1 2 3 4 5 6 7 8 9 10 1234567890轉字串:1234567890 -123456789轉字串:-123456789 8976543210123456789轉字串:8976543210123456789 -897654321012345678轉字串:-897654321012345678 int型的數值範圍是:-2147483648,2147483647 long int型的數值範圍:-2147483648,2147483647 long long型的數值範圍:-9223372036854775808,9223372036854775807 -------------------------------- Process exited after 0.5405 seconds with return value 0 請按任意鍵繼續. . .
只是測試一下,因為庫函式to_string()轉int成字串是非常好用的。但是它轉float\double型用處不大,其返回的小數部分只保留6位,即小於0.000001的數都轉成0.000000,要麼四捨五入成0.000001。float\double的數還是用stringstream來轉比較方便。