C语言 使用 scanf 进入无限循环

Question

所以我有一些这样的代码(请注意这是在C89中(：

void inputChoice(int* choicePtr)
{
int choice;
printf(BLUE "nINPUT: " RESET);                     /* Print input using the ansi colour code for Blue. */
scanf("%d", &choice);                               /* Parse the choice. */
while ((choice < 1) && (choice > 5))                /* Loop until choice is one of the menu options. */
{
/* Request for a valid menu option, printing this using the ansi colour code for Red, then resetting back to the default colour. */
printf(RED "nMenu Selection must be between (1 and 5) inclusive. nPlease Re-enter. n" RESET);
scanf("%d", &choice);                           /* Parse the choice. */
}
*choicePtr = choice;                                /* Set the choice pointer to the valid choice after validation. */
}

哪个得到选择。它适用于整数。但是如果有人输入其他内容，例如角色。它无限循环。 我想以某种方式检查是否输入了字符。

我尝试这样做的一种方法是添加它来检查是否输入了字符，因为如果整数没有正确扫描，整数将为 0。

如下所示，但这也不起作用：

scanf("%d", &choice);
while (choice == 0)
{
printf("Invalid Choice Re-enter.");
scanf("%d", &choice);
}

Answer 1

表达式

while ((choice < 1) && (choice > 5))  

永远不会为真，因为choice不能大于5小于1。

您将需要：

while (choice < 1 || choice > 5) 

scanf将尝试解析缓冲区上是否有任何内容但无法解析，它将继续尝试导致无限循环，因为缓冲区中的任何内容都将保留在那里，直到成功解析为止。

由于如果没有解析参数，scanf将返回0，因此您可以使用该信息清除缓冲区，删除导致无限循环的原因：

int choice = 0;
int c; 
int scanned;
//...
if ((scanned = scanf("%d", &choice)) == EOF){ //check for EOF return
puts("Unexpected error.");       
//error treatment is upt to you, I would avoid the loop
*choicePtr = scanned;
return;
}
if (scanned == 0) {
while ((c = fgetc(stdin)) != 'n' && c != EOF){}
}

在两个scanfS。

现场演示

Answer 2

考虑到评论中的评论，下面是一个修改版本：

/* reading an input choice between 1 and 5 or -1 on error */
void inputChoice(int *choicePtr) {
int choice;
printf(BLUE "nINPUT: " RESET);       /* Print input using the ansi colour code for Blue. */
for (;;) {
int res = scanf("%d", &choice);   /* Parse the choice. */
if (res == EOF) {
printf(RED "unexpected end of filen" RESET);
choice = -1;
break;
}
if (res == 0) {
int c;
while ((c = getchar()) != EOF && c != 'n')
continue;
printf(RED "invalid entryn" "Please Re-enter.n" RESET);
continue;
}
if (choice >= 1 && choice <= 5) {
break;
}
/* Loop until choice is one of the menu options. */
/* Request for a valid menu option, printing this using the ansi 
colour code for Red, then resetting back to the default colour. */
printf(RED "nMenu Selection must be between (1 and 5) inclusive.n"
"Please Re-enter.n" RESET);
}
/* Set the choice pointer to the valid choice after validation. */
*choicePtr = choice;
}