static variable scope inside and outside the function

debugcn Published at Dev

user1323328

Please notice the static variable selection. I am testing if the selection is assigned the correct char string within the different scope.

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

static char* selection;

static char* sel_item(char* text)
{
    char* pch;
    char buf[80];
    strcpy(buf, text);
    pch = strtok(buf, " ");
    return pch;
}

static int display_ecnt_codes(char* text)
{   
    char buf[80];
    strcpy(buf, text); 
    selection = sel_item(buf);
    // why if I output the selection here, the selection is random char, not the correct char "SRFPRO".
    // printf("display_ecnt_codes: %s\n", selection); 
}

int acode_prockey()
{
    char text[] = "SRFPRO - Surface Protection (DealerProduct)";
    display_ecnt_codes(text); 
    // why if I output the selection here, it prints the correct char string "SRFPRO".
    // what's the difference between this scope and the above scope?
    printf("acode_prockey: %s\n", selection); 
}

int main ()
{
    acode_prockey();
    // it will output SRFPRO, the first token of the char text[].
    printf("main: %s\n", selection);  
}

I am hoping someone can explain the global static varible "selection". When I printf it inside the function "display_ecnt_codes", it outputs the random char. If I do not printf it inside the function, it output the correct char in the main function.

R Sahu

In the following function, you are returning a pointer that is not valid after the function returns.

static char* sel_item(char* text)
{
    char* pch;

    // An array on the stack
    char buf[80];
    strcpy(buf, text);

    // A pointer to some element of the array.
    pch = strtok(buf, " ");

    // Returns a pointer that is not valid after the function returns.
    return pch;
}

Later on, you use that invalid pointer which is stored in selection. Your program exhibits undefined behavior because of that.

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edited at2021-07-9

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