C空字符导致程序行为问题
我遇到的问题是这个程序是菜单驱动的。 当我输入字母时，“i”被输入到input数组中，其大小为MAX_LENGTH+1 。 通过GDB，我发现input数组的第0个索引输入“i”，其余空格输入NULL_CHAR字符。 无论如何，当我按下“i”作为插入菜单时，我向一个字段打招呼，告诉我输入一个值。 我输入任何整数并按inter。 它没有受到“命令？：”字段的欢迎，而是给我一个输入条目的机会，它立即告诉我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 ，可能是因为输入char数组中的所有其他值将所有其他条目作为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，因为有一个语句c = getchar()应该再次询问我的输入。 但由于某些原因，在每个条目之后， c的默认值变为NULL_CHAR，并在下次调用safegets时要求您输入。
这是我想要的输出结果如下：
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:
这是主要function：
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; }
你的代码很好。 你需要改变
scanf("%d", value); // ^Place & before the argument value because scanf expect pointer as its argument
至
scanf("%d", &value);
如果修复ze代码费用
else { // do this if no command matched ... if (response != '\0') printf("\nInvalid command.\n%s\n",commandList); }
我相信你的代码的问题是你在调用scanf之后没有清空输入缓冲区（例如if和’I’被输入并且’value’被读取。在每次调用scanf你仍然会有回车符和/或输入缓冲区中的换行符。下一次对safegets调用看到输入仍在输入缓冲区中并读取它。要修复它，在每次调用scanf后清空输入缓冲区：
char strip; . . . if (response == 'I') { printf(" value: "); scanf("%d", value); /* empty the input buffer after scanf */ do { strip = getchar(); } while (strip != '\n'); printf }