C语言中的令牌读取困难

Question

I can't seem to figure out, how to correctly read in a .txt file that has the following appereance: (example)

+ 1
+ 2
- 2
+ 5
p -1
? 5

and so on... what I need now is to store the operator / token which can be '+' '-' 'p' or something like that, and the int that follows in two different variables because I need to check them later on.

char oprtr[1];
int value;
FILE *fp = fopen(args[1], "r");

while(!feof(fp) && !ferror(fp)){
    if(fscanf(fp, "%s %d\n", oprtr, &value) < 1){
        printf("fscanf error\n");
    }
    if(strcmp(oprtr, "+") == 0){
        function1(bst, value);

    } else if(strcmp(oprtr, "-") == 0){
        function2(bst, value);

    } else if((strcmp(oprtr, "p") == 0) && value == -1){
        function3(root);
    //some other functions and so on...
    }

printing out oprtr and value in the loop shows that they are not being red in correctly, but it does compile. Does someone have a solution?

Answer 1

You have single characters, you can use == to compare them instead of strcmp . Just read the input in pairs and use a switch for example.

char c;
int x;

while(fscanf(fp, "%c %d", &c, &x) == 2)
{   switch(c)
    {   case '+': /* ... */
    }
}

Answer 2

Your string oprtr is too small to hold anything but an empty string (remember that C strings need a terminating 0 character!). So:

char oprtr[1];

needs to be at least:

char oprtr[2];         // string of maximum size 1

or more defensively:

char oprtr[256];       // string of maximum size 255

Answer 3

You can use the fscanf function, you can get the input from the file.

int fscanf(FILE *stream, const char *format, ...);

fscanf(fp," %c %d",&c,&d);