所以我想为一个程序做一个简单的菜单,只接受选项1,2和3,我想控制用户输入,以防止错误,比如当用户输入char而不是int时。
现在它控制了一些情况,比如如果选项小于1或大于3,如果选项是char,它也不会影响,但是当用户输入诸如 "02 "或 "2a "时,它会运行选项2,但应该使该选项无效。
另外,如果有更多我遗漏的情况,我想知道它们以及如何克服它们。
#include <stdio.h>
#include <stdlib.h>
void empty_stdin(void);
int main() {
int option;
int rtn;
do {
printf("\n--\nOptions:\n1.Option 1\n2.Option 2\n3.Option 3\n--\n\nPlease chose option (1/2/3) to continue: ");
rtn = scanf("%d", &option);
if (rtn == 0 || option < 1 || option > 3) {
printf("-Invalid Option-\n");
empty_stdin();
} else {
empty_stdin();
switch (option) {
case 1:
printf("Option 1");
break;
case 2:
printf("Option 2");
break;
case 3:
printf("Option 3");
exit(0);
default:
printf("\n-Invalid Option-\n");
}
}
} while (option != 3);
return 0;
}
void empty_stdin(void) {
int c = getchar();
while (c != '\n' && c != EOF)
c = getchar();
}
输入输出示例
--
Options:
1.Option 1
2.Option 2
3.Option 3
--
Please chose option (1/2/3) to continue: 1
Option 1
--
Options:
1.Option 1
2.Option 2
3.Option 3
--
Please chose option (1/2/3) to continue: 12
-Invalid Option-
--
Options:
1.Option 1
2.Option 2
3.Option 3
--
Please chose option (1/2/3) to continue: char
-Invalid Option-
--
Options:
1.Option 1
2.Option 2
3.Option 3
--
Please chose option (1/2/3) to continue: 02
Option 2
--
Options:
1.Option 1
2.Option 2
3.Option 3
--
Please chose option (1/2/3) to continue: 2a
Option 2
--
Options:
1.Option 1
2.Option 2
3.Option 3
--
Please chose option (1/2/3) to continue: 02a
Option 2
--
Options:
1.Option 1
2.Option 2
3.Option 3
--
预期的输入输出
--
Options:
1.Option 1
2.Option 2
3.Option 3
--
Please chose option (1/2/3) to continue: 1
Option 1
--
Options:
1.Option 1
2.Option 2
3.Option 3
--
Please chose option (1/2/3) to continue: 12
-Invalid Option-
--
Options:
1.Option 1
2.Option 2
3.Option 3
--
Please chose option (1/2/3) to continue: char
-Invalid Option-
--
Options:
1.Option 1
2.Option 2
3.Option 3
--
Please chose option (1/2/3) to continue: 02
-Invalid Option-
--
Options:
1.Option 1
2.Option 2
3.Option 3
--
Please chose option (1/2/3) to continue: 2a
-Invalid Option-
--
Options:
1.Option 1
2.Option 2
3.Option 3
--
Please chose option (1/2/3) to continue: 02a
-Invalid Option-
--
Options:
1.Option 1
2.Option 2
3.Option 3
--
考虑使用 fgets
以获取输入和 strtol
来解析一个整数。
#include <stdio.h>
#include <stdlib.h>
#include <errno.h>
#include <limits.h>
int fgetsint ( int *value, int min, int max, FILE *fin) {
char line[100] = "";
char extra = '\0';
char *end = NULL;
long int number = 0;
if ( fgets ( line, sizeof line, fin)) {//read a line
errno = 0;
number = strtol ( line, &end, 10);
if ( end == line) {// nothing was parsed. no digits
printf ( "input [%s] MUST be a number\n", line);
return 0;// return failure
}
if ( ( errno == ERANGE && ( number == LONG_MAX || number == LONG_MIN))
|| ( errno != 0 && number == 0)) {// parsing error from strtol
perror ( "input error");
return 0;
}
if ( 1 == sscanf ( end, " %c", &extra)) {//parse trailing character
printf ( "enter one number only. try again\n");
return 0;
}
if ( number > max || number < min) {
printf ( "Input [%ld] out of range: min: %d max: %d\n", number, min, max);
return 0;
}
if ( 1 != (int)( end - line)) {
printf ( "input one digit\n");
return 0;// return failure
}
*value = number;//assign number to pointer
}
else {
fprintf ( stderr, "problem fgets\n");
exit ( EXIT_FAILURE);
}
return 1;//success
}
int main ( void) {
int option = 0;
do {
printf("\n--\nOptions:\n1.Option 1\n2.Option 2\n3.Option 3\n--\n\nPlease chose option (1/2/3) to continue: ");
option = 0;
fgetsint ( &option, 1, 3, stdin);
switch (option) {
case 1:
printf("Option 1");
break;
case 2:
printf("Option 2");
break;
case 3:
printf("Option 3");
exit(0);
default:
printf("\n-Invalid Option-\n");
}
} while ( option != 3);
return 0;
}
下面建议的代码。
现在,拟议的守则。
#include <stdio.h>
void empty_stdin( void );
int main( void )
{
int option = 9;
do
{
printf("\n--\nOptions:\n"
"1.Option 1\n"
"2.Option 2\n"
"3.Option 3\n"
"--\n\n"
"Please chose option (1/2/3) to continue: ");
option = getchar();
empty_stdin();
switch (option)
{
case 1:
printf( "Option 1\n" );
break;
case 2:
printf( "Option 2\n" );
break;
case 3:
printf( "Option 3, exiting\n" );
//exit(0);
break;
default:
printf( "\n-option: %d invalid-\n", option );
break;
}
} while ( option != 3 && option != EOF );
return 0;
}
void empty_stdin( void )
{
//int c = getchar();
//while (c != '\n' && c != EOF)
//c = getchar();
int c;
while( (c = getchar() ) != EOF && c != '\n' );
}