Infinite Loop in Tokenizing Input

Question

Good afternoon everybody, I am working with tokenizing input in C for a dummy shell program and I am having problems with an infinite loop. In my example code, workwithtokenstuff() is executing infinitely. I have formed similar loops before, I am not sure why the scanf at the bottom is being skipped. Example input is "cd /dummydir". I have another strtok() call to split the dir into another char array.

char inStr[255];
char *token;

scanf("%[^\n\r]", inStr);
token = strtok(inStr, " ");
while (strcmp(token, "exitcom") != 0) {
    workwithtokenstuff();

    scanf("%[^\n\r]", inStr);
    token = strtok(inStr, " ");
}

Answer 1

The second scanf is not really skipped, it's catching the newline character left on the input buffer by the previous scanf, a space before the specifier is a usual fix, it consumes whitespace characters present in the buffer.

char inStr[255];
char *token;

scanf("%254[^\n\r]", inStr);  // note the width limit, avoids buffer overflow

token = strtok(inStr, " ");
while (strcmp(token, "exitcom") != 0)
{
    workwithtokenstuff(); // assuming this does not consume any more tokens
    scanf(" %254[^\n\r]", inStr);
    //     ^ space here
    token = strtok(inStr, " ");
}

Footnotes:

• For a more robust code, checking the return value of scanf is advised.

• Maybe you are aware of this, but nonetheless I'll mention that strtok, among other things, changes the original string. If you need more details check How does the strtok function in C work?.