Access the next word/string - c

Question

I have a simple C-based code to read a file. Read the input line by line. Tokenize the line and prints the current token. My problem is, I want to print the next token if some conditions are satisfied. Do you have any idea how to do it. I really need your help for this project. Thank you
Here is the code:
main(){
FILE *input;
FILE *output;
//char filename[100];
const char *filename = "sample1.txt";
input=fopen(filename,"r");
output=fopen("test.st","w");
char word[1000];
char *token;
int num =0;
char var[100];
fprintf(output,"LEXEME, TOKEN");
while( fgets(word, 1000, input) != NULL ){ //reads a line
token = strtok(word, " \t\n" ); // tokenize the line
while(token!=NULL){ // while line is not equal to null
fprintf(output,"\n");
if (strcmp(token,"SIOL")==0)
fprintf(output,"SIOL, SIOL", token);
else if (strcmp(token,"DEFINE")==0)
fprintf(output,"DEFINE, DEFINE", token);
else if (strcmp(token,"INTEGER")==0){
fprintf(output,"INTEGER, INTEGER");
strcpy(var,token+1);
fprintf(output,"\n%s,Ident",var);
}
else{
printf("%s\n", token);
}
token = strtok(NULL, " \t\n" ); //tokenize the word
}}fclose(output);return 0;}

Answer 1

Continuing from my comment. I'm not sure I completely understand what you need, but if you have the string:
"The quick brown fox";
And, you want to tokenize the string, printing the next word, only if a condition concerning the current word is met, then you need to adjust your thinking just a bit. In your example, you want to print the next word "quick", only if the current word is "The".
The adjustment in thinking is how you look at the test. Instead of thinking about printing the next word if the current matches some condition, you need to save the last word, and only print the current if the last word matches some condition -- "The" in your example.
To handle that situation, you can make use of a statically declared character array of at least 47 characters (the longest word in Merriam-Websters Unabridged Dictionary is 46-character). I'll use 48 in the example below. You may be tempted to just save a pointer to the last word, but when using strtok there is no guarantee that the memory address returned by the previous iteration is preserved -- so make a copy of the word.
Putting the pieces together, you could do something like the following. It saves the prior token in last and then compares the current word to the last and prints the current word if last == "The":
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#define MAXW 48
int main (void) {
char str[] = "The quick brown fox";
char last[MAXW] = {0};
char *p;
for (p = strtok (str, " "); p; p = strtok (NULL, " "))
{
if (*last && strcmp (last, "The") == 0)
printf (" '%s'\n", p);
strncpy (last, p, MAXW);
}
return 0;
}
Output
$ ./bin/str_chk_last
'quick'
Let me know if you have any questions.
Test Explanation
As written in the comment *last is simply shorthand for last[0]. So the first part of the test, *last is just testing if ((last[0] != 0) && ... Since last was initially declared and initialized:
char last[MAXW] = {0};
All chars in last are 0 for the first pass through the loop. By including the check last[0] != 0, that just causes the printf to be skipped the first time the for loop executes. The longhand for the test would look like:
if ((last[0] != 0) && strcmp (last, "The") == 0)
printf (" '%s'\n", p);
Which in pseudo code just says:
if (NOT first iteration && last == "The")
printf (" '%s'\n", p);
Let me know if that doesn't make sense.

Answer 2

It is easy to achieve with strtok function. Note that if you put null pointer as the first argument, the function continues scanning the same string where a previous successful call to the function ended. So if you need next token just call
char* token = strtok(NULL, delimeters);
See small example below
#include <stdio.h>
#include <string.h>
int main(void)
{
char str[] = "The quick brown fox";
// split str by space
char* token = strtok(str, " ");
// if a token is found
if(token != NULL) {
// print current token
printf("%s\n", token);
// if token is "The"
if(strcmp(token, "The") == 0) {
// print next token
printf("%s\n", strtok(NULL, " "));
}
}
return 0;
}
The output will be
The
quick