C数据输入（输出）from（to）keyboard（screen）filestring

　　C和C++中有三类输入输出操作：
　　standard I/O（标准 I/O），通常是指用键盘做入输入，显示屏做为输出；
　　file I/O（文件I/O），硬盘文件既可以是数据输入源，也可以是输出的去向。
　　string(in-memory)（字符串 I/O），也就是可以将一个字符串做输入的数据源或将字符串做为数据的一个输出去向。1 standard Input and Output
　　示例1，输入检查：#include  int main(void) {     int num;     int status;     printf(＂input the value of num:＂);     status = scanf(＂%d＂,&num);     if(status ==0)     {         printf(＂enter error＂);         fflush(stdin);//清除输入缓冲区的错误数据      }     else if(status == EOF)     {         printf(＂Input failure occurs! ＂);      }          else         printf(＂ num = %d ＂,num);     fflush(stdin);     getchar();          return 0; }
　　可以用成以下do while，用于正确输入：#include  int main(void) {     int num;     int status;     printf(＂input the value of num:＂);     do{         status = scanf(＂%d＂,&num);         fflush(stdin);     }while(status==0 || status == EOF);     printf(＂%d ＂,num);     getchar();getchar();     return 0; }
　　示例2，do…while用于交互：#include  #include   int main() {  	char rsp;     do {         printf(＂please enter two values: ＂);         int val1, val2;         scanf(＂%d %d＂,&val1,&val2);         printf(＂%d + %d = %d ＂,val1,val2,val1+val2);         printf(＂More? [y][n] ＂);         getchar(); // 接收 字符         scanf(＂%c＂,&rsp);     } while (rsp == ＂y＂ || rsp == ＂Y＂); }
　　示例3，cin输入跳过非数字字符:// non-numeric input skipped #include  const int Max = 5; int main() {     using namespace std;     // get data     int golf[Max];     cout << ＂Please enter your golf scores. ＂;     cout << ＂You must enter ＂ << Max << ＂ rounds. ＂;     int i;     for (i = 0; i < Max; i++)     {         cout << ＂round #＂ << i+1 << ＂:＂ ;         while (!(cin >> golf[i])) {             cin.clear(); // reset input             while (cin.get() != ＂ ＂)  // ignore                 continue; // get rid of bad input             cout << ＂Please enter a number:＂;         }     }     // calculate average     double total = 0.0;     for (i = 0; i < Max; i++)         total += golf[i];     // report results     cout << total / Max << ＂ = average score ＂         << Max << ＂ rounds ＂;     getchar();getchar();     return 0; } /* Please enter your golf scores. You must enter 5 rounds. round #1:87 round #2:78 round #3:a Please enter a number:66 round #4:+ Please enter a number:99 round #5:75 81 = average score 5 rounds */2 file Input and Output
　　示例代码，文件复制：#include  #include   void file_copy(FILE * , FILE * );  int main( void ) { 	FILE *abc; 	FILE *abc_b; 	if((abc = fopen(＂D:abc.TXT＂,＂rb＂)) == NULL ) 	{ 		printf(＂打开文件失败 ＂); 		return EXIT_FAILURE; 	} 	if((abc_b = fopen(＂D:ABC_B.TXT＂,＂wb＂)) == NULL ) 	{ 		printf(＂打开文件失败 ＂); 		return EXIT_FAILURE; 	}  	file_copy( abc_b , abc ); 	if( feof(abc) != 0 ) 	{ 		printf(＂拷贝正常结束 ＂); 		fclose(abc); 		fclose(abc_b); 		return EXIT_SUCCESS; 	}  	if( ferror (abc) != 0 ) 	{ 		printf(＂拷贝过程中发生错误，目标文件可能并不正确 ＂); 		fclose(abc); 		fclose(abc_b); 		return EXIT_FAILURE; 	} }  void file_copy( FILE * t, FILE *s ) { 	int ch; 	while( (ch = fgetc(s) ) != EOF ) 		fputc( ch , t ); }3 string(in-memory) Input and Output
　　C语言的sscanf()和sprintf()：#include     int main( void )  {      char  tokenstring[] = ＂15 12 14...＂;      char  s[81]={0};      char  c;      int   i;      float fp;      sscanf( tokenstring, ＂%80s＂, s );      // 以字符串作为数据输入源，分解字符串      sscanf( tokenstring, ＂%c＂, &c );      sscanf( tokenstring, ＂%d＂, &i );      sscanf( tokenstring, ＂%f＂, &fp );      char str[222] = {0};      sprintf(str,＂%s %c %d %f ＂,s,c,i,fp); // 以字符串作为数据输出出身，组装字符串      printf( ＂%s＂, str);      sscanf( tokenstring,＂%d %f＂,&i,&fp);// 以字符串作为数据输入源，分解字符串      sprintf(str,＂%d,%f ＂,i,fp);       // 以字符串作为数据输出出身，组装字符串      printf( ＂%s＂, str); 	 getchar();      return 0;   }
　　C++语言的istringstream：#include  #include  #include  using namespace std;  int main() {    string input( ＂Input test 123 4.7 A＂ );    istringstream inputString( input );    string string1;    string string2;    int integer;    double double1;    char character;     inputString >> string1 >> string2 >> integer >> double1 >> character;     cout << ＂The following items were extracted ＂       << ＂from the istringstream object:＂ << ＂ string: ＂ << string1       << ＂ string: ＂ << string2 << ＂    int: ＂ << integer       << ＂ double: ＂ << double1 << ＂   char: ＂ << character;     // attempt to read from empty stream    long value;    inputString >> value;     // test stream results    if ( inputString.good() )       cout << ＂  long value is: ＂ << value << endl;    else       cout << ＂  inputString is empty＂ << endl; }
　　C++语言的ostringstream：#include  #include  #include  // header file for string stream processing using namespace std;  int main() {    ostringstream outputString; // create ostringstream instance     string string1( ＂Output of several data types ＂ );    string string2( ＂to an ostringstream object:＂ );    string string3( ＂         double: ＂ );    string string4( ＂            int: ＂ );    string string5( ＂ address of int: ＂ );     double double1 = 123.4567;    int integer = 22;     // output strings, double and int to ostringstream outputString             outputString << string1 << string2 << string3 << double1         << string4 << integer << string5 << &integer;     // call str to obtain string contents of the ostringstream    cout << ＂outputString contains: ＂ << outputString.str();     // add additional characters and call str to output string    outputString << ＂ more characters added＂;    cout << ＂  after additional stream insertions, ＂       << ＂outputString contains: ＂ << outputString.str() << endl; }
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