使用strcmp的分段错误（Ubuntu）

Question

I have the following code segment:

token = strtok(line, separator);
i = 0;
args[i++] = token;  /* build command array */
while( token != NULL ) /* walk through other tokens */
{
    /* printf( " %s\n", token ); */
    token = strtok(NULL, separator);
    if (strcmp(token, "|") != 0) {
        printf("entered");
    }
    else {
        args[i++] = token;
    }   /* and build command array */

The code compiles fine, but upon execution passing any argument, I receive the error "Segmentation fault (Core dumped)". Removing the if statement comparing the 2 strings solves the issue, so it is a problem with that comparison.

Answer 1

When strtok does not find next token it returns NULL , thus the segfault when trying to strcmp(NULL, "|")

Test if token is null before strcmp .

Answer 2

the posted code:

token = strtok(line, separator);
i=0;
args[i++]=token;  /* build command array */
while( token != NULL ) /* walk through other tokens */
{
  /* printf( " %s\n", token ); */
  token = strtok(NULL, separator);
  if (strcmp(token, "|") != 0) {
      printf("entered");
  }
  else {
      args[i++] = token;
  }   /* and build command array */

contains a logic error. the returned value from strtok() is being used before being checked.

suggest something similar to:

i=0;
token = strtok(line, separator);

while( token != NULL ) /* walk through other tokens */
{
    /* printf( " %s\n", token ); */
    if (strcmp(token, "|") != 0)
    {
        printf("entered");
    }

    else
    {
        args[i++] = token;
    }   /* and build command array */

    ...
    token = strtok(NULL, separator);
} // end while