我很久没用过 C 了，显然我忘记的比我想象的要多。在尝试使用 malloc() 分配字符串时，我不断获取该字符串的旧数据，包括它的旧数据，当请求的空间较短时长度较长。这种情况确实包括指向被 free()'d 并设置为 NULL 的字符串的指针。这是我在终端中看到的示例运行：
yes, quit, or other (<-message from program)
oooo (<-user input; this will be put to upper case and token'd)
------uIT LENGTH:4 (<-debug message showing length of userInputToken)
preC--tmp: (<-contents of tmp variable)
pstC--tmp:OOOO (<-contents of temp variable)
bad input (<-program response)
yes, quit, or other
yes
------uIT LENGTH:3
preC--tmp:OOOO (<-: tmp = malloc(sizeof(char)*(strlen(userInputToken)-1)); )
pstC--tmp:YESO (<-: strncpy(tmp,userInputToken,strlen(userInputToken)-1); )
bad input
yes, quit, or other
yes
------uIT LENGTH:3
preC--tmp:YESO
pstC--tmp:YESO
bad input
yes, quit, or other
quit
------uIT LENGTH:4
preC--tmp:YESO
pstC--tmp:QUIT (<-: Successful quit because I only did 4 chars; if 5 were used, this would have failed)
如您所见， strlen(userInputToken) 获得了正确的长度，并用于获取正确数量的复制字符——但无论是 free() 还是 malloc() 似乎都不关心它。我无法弄清楚这里发生了什么！这是将 C 留给 Python 的惩罚吗？
更重要的是，应该清除 tmp 变量，而不管 free() 是什么，因为它受到其范围的限制。这是一切都失败的代码：
在 main.c 中：
void run() {
outputFlagContainer *outputFlags = malloc(sizeof(outputFlagContainer));
while(true) {
puts("yes, quit, or other");
outputFlags = getUserInput(outputFlags);
if (outputFlags->YES) {
puts("It was a yes!");
} else if (outputFlags->QUIT) {
break;
} else {
puts("bad input");
}
}
free(outputFlags);
}
在 messageParserPieces.h 中：
outputFlagContainer *getUserInput(outputFlagContainer *outputFlags) {
outputFlags = resetOutputFlags(outputFlags);
char *userInput = NULL;
char user_input[MAX_INPUT];
char *userInputToken = NULL;
char *tmp = NULL;
char *finalCharacterCheck = NULL;
// Tokens to search for:
char QUIT[] = "QUIT";
char YES[] = "YES";
userInput = fgets(user_input, MAX_INPUT-1, stdin);
int i = 0;
while(userInput[i]) {
userInput[i] = toupper(userInput[i]);
i++;
}
userInputToken = strtok(userInput, " ");
if (userInputToken) {
finalCharacterCheck = strchr(userInputToken, '\n');
if (finalCharacterCheck) {
int MEOW = strlen(userInputToken)-1; // DEBUG LINE
printf("\n------uIT LENGTH:%d\n", MEOW); // DEBUG LINE
// The problem appears to happen here and under the circumstances that
// userInput is (for example) 4 characters and then after getUserInput()
// is called again, userInput is 3 characters long.
tmp = malloc(sizeof(char)*(strlen(userInputToken)-1));
if (tmp == NULL) {
exit(1);
}
printf("\npreC--tmp:%s\n", tmp); // This shows that the malloc DOES NOT use the given length.
strncpy(tmp,userInputToken,strlen(userInputToken)-1);
printf("\npstC--tmp:%s\n", tmp); // Copies in the correct number of characters.
userInputToken = tmp;
free(tmp);
tmp = NULL;
}
}
while (userInputToken != NULL) { // NULL = NO (more) tokens.
if (0 == strcmp(userInputToken, YES)) {
outputFlags->YES = true;
} else if (0 == strcmp(userInputToken, QUIT)) {
outputFlags->QUIT = true;
}
userInputToken = strtok(NULL, " ");
if (userInputToken) {
finalCharacterCheck = strchr(userInputToken, '\n');
if (finalCharacterCheck) {
tmp = malloc(sizeof(char)*(strlen(userInputToken)-1));
if (tmp == NULL) {
exit(1);
}
strncpy(tmp,userInputToken,strlen(userInputToken)-1);
userInputToken = tmp;
free(tmp);
tmp = NULL;
}
}
}
return outputFlags;
}
我假设这是某种明显的错误，但我今晚尝试用谷歌搜索它大约 2 小时。我想不出如何搜索这个不带 malloc() 教程的东西——我已经看过几个了。
任何见解都将不胜感激！