c - 神奇的段错误？

Question

我查看了网站上的其他类似问题，但我仍然看不出我遗漏了什么。 C 对我来说是一个新的可怕的野兽，所以我确信它很简单，但是当代码到达while 循环。

我尝试将一个字符串直接写入 currentInput 而仍然得到它，所以我认为我以某种方式访问​​了该字符串错误？

我的理解是，段错误是由访问(程序？)无法访问的内存引起的...

顺便说一句，有没有办法在 strcmp(); 中使用字符串文字？所以我可以比较“END”？

void runCommands()
{
    char * currentInput = (char*)malloc(100); //100 char input buffer
    char * cmd = (char*) malloc(CMD_LENGTH);
    char * target = (char*) malloc(UID_LENGTH);
    char * key = (char*) malloc(KEY_LENGTH);
    char * endstr = "END";
    cmd = "UNDEF";
    target = "UNDEF";
    key = "UNDEF";
    ushort tokens;

    while (strcmp(cmd, endstr) != 0) //Run until command is "END"
    {
        printf("ENTER INSTRUCTION: ");
        fgets(currentInput, sizeof(currentInput), stdin); //FAULT OCCURS HERE
        tokens = sscanf(currentInput, "%[^,\n],%[^,\n],%s", cmd, target, key); //parse string for values
        if (tokens <= 3 && tokens >= 1) //ensure valid # of tokens passed
        {
            fprintf(stdout, "TOKENS:\nCMD: %s\ntarget: %s\nkey: %s\n", cmd, target, key);
            switch (tokens)
            //restore UNDEF for non-existent tokens
            {
            case 1:
                target = "UNDEF";
                /* no break */
            case 2: //intentional fallthrough
                key = "UNDEF";
                break;
            default:
                break;
            }
            /* handle commands */
            if (strcmp(cmd, endstr) == 0)
            {
                end(keyfile);
            } //write file and exit function
            else if (strcmp(cmd, "DELETE") == 0)
            {
                delete(target, key);
            } //delete specified key from UID
            else if (strcmp(cmd, "VALIDATE") == 0)
            {
                validate(target, key);
            } //valid/not valid based on key presence
            else if (strcmp(cmd, "ADD") == 0)
            {
                add(target, key);
            } //add key to target UID
            else if (strcmp(cmd, "PRINT") == 0)
            {
                print(target);
            } //print sorted keys for UID or all keys for ALL
            else
            {
                invalidCMD(cmd);
            } //error message for invalid command
        }
        else
        {
            invalidCMD(currentInput); //use whole input as bad command if invalid format
        }
    }
    free(currentInput);
    free(target);
    free(key);
    free(cmd);
}

Answer 1

您通过覆盖 malloc 返回的指针值导致内存泄漏和未定义的行为:

char * currentInput = (char*)malloc(100); //100 char input buffer
char * cmd = (char*) malloc(CMD_LENGTH);
char * target = (char*) malloc(UID_LENGTH);
char * key = (char*) malloc(KEY_LENGTH);
//...
// This is where you cause the issue
char * endstr = "END";
cmd = "UNDEF";
target = "UNDEF";
key = "UNDEF";

由于您切断了代码，我无法评论您的其余代码以确定还有什么会导致问题。

一件事是您肯定没有正确使用 sizeof()，因为 sizeof(currentInput) 等于 sizeof(char*)，而不是字符串的长度。