【发布时间】：2014-06-26 04:21:48
【问题描述】：
我遇到的问题是这个程序是菜单驱动的。当我输入字母“i”时，将输入input 数组，其大小为MAX_LENGTH+1。通过GDB我发现“i”输入到input数组的第0个索引中，其余空格输入NULL_CHAR字符。无论如何，当我为插入菜单按“i”时，我看到了一个告诉我输入值的字段。我输入任何整数并按inter。它没有受到“命令？：”字段的欢迎并给我一个输入条目的机会，而是立即告诉我我的输入无效并告诉我再次输入命令。这就是我的意思：
Commands are I (insert), D (delete), S (search by name),
V (search by value), P (print), Q (quit).
Command?: i
45
Command?:
Invalid command.
Commands are I (insert), D (delete), S (search by name),
V (search by value), P (print), Q (quit).
Command?:
我发现发生这种情况的原因是因为当再次调用safegets函数时，由于某种原因，函数safegets中的局部变量c的值为NULL_CHAR，大概是因为所有的输入字符数组中的其他值的所有其他条目为NULL_CHAR。我不明白为什么c 会自动分配NULL_CHAR 的值，因为在while 循环中，因为有一条语句c = getchar() 应该再次要求我输入。但是由于某种原因，在每次输入之后，c 的默认值变为 NULL_CHAR，并在下次调用 safegets 时要求您输入。
这是我想要的输出：
Commands are I (insert), D (delete), S (search by name),
V (search by value), P (print), Q (quit).
Command?: I
value: 50000
Command?: I
value:
这里是主要功能：
const int MAX_LENGTH = 1023;
const char NULL_CHAR = '\0';
const char NEWLINE = '\n';
int main (void)
{
const char bannerString[]
= "Personal Team Maintenance Program.\n\n";
const char commandList[]
= "Commands are I (insert), D (delete), S (search by name),\n"
" V (search by value), P (print), Q (quit).\n";
// Declare linked list head.
// ADD STATEMENT(S) HERE TO DECLARE LINKED LIST HEAD.
// announce start of program
printf("%s",bannerString);
printf("%s",commandList);
char response;
char input[MAX_LENGTH+1];
int value;
do
{
printf("\nCommand?: ");
safegets(input,MAX_LENGTH+1);
// Response is first char entered by user.
// Convert to uppercase to simplify later comparisons.
response = toupper(input[0]);
if (response == 'I')
{
// Insert a player entry into the linked list.
// Maintain the list in correct order (G, D, M, S).
// ADD STATEMENT(S) HERE
// USE THE FOLLOWING PRINTF STATEMENTS WHEN PROMPTING FOR DATA:
// printf(" family name: ");
// printf(" first name: ");
// printf(" position: ");
printf(" value: ");
scanf("%d", value);
}
else if (response == 'D')
{
// Delete a player from the list.
printf("\nEnter family name for entry to delete: ");
// ADD STATEMENT(S) HERE
}
else if (response == 'S')
{
// Search for a player by family name.
printf("\nEnter family name to search for: ");
// ADD STATEMENT(S) HERE
}
else if (response == 'V')
{
// Search for players that are worth less than or equal a value.
printf("\nEnter value: ");
// ADD STATEMENT(S) HERE
}
else if (response == 'P')
{
// Print the team.
// ADD STATEMENT(S) HERE
}
else if (response == 'Q')
{
; // do nothing, we'll catch this case below
}
else
{
// do this if no command matched ...
printf("\nInvalid command.\n%s\n",commandList);
}
} while (response != 'Q');
// Delete the whole linked list that hold the team.
// ADD STATEMENT(S) HERE
// Print the linked list to confirm deletion.
// ADD STATEMENT(S) HERE
return 0;
}
正在调用的辅助函数：
void safegets (char s[], int arraySize)
{
int i = 0, maxIndex = arraySize-1;
char c;
while (i < maxIndex && (c = getchar()) != NEWLINE)
{
s[i] = c;
i = i + 1;
}
s[i] = NULL_CHAR;
}
【问题讨论】：
-
您为什么要尝试将
\0和\n隐藏在一些自定义名称后面？虽然避免使用魔法常数是一种很好的做法，但它们并非如此。 -
这通常不称为“空字符”，而是“终止空字符”。
-
请只提供最少量的代码来证明您的问题。