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more on struct.

This is a discussion on more on struct. within the C Programming forums, part of the General Programming Boards category; how to print struct from another function? let's say I have code this way Code: struct student{ int id // ...

  1. #1
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    more on struct.

    how to print struct from another function?
    let's say I have code this way
    Code:
    struct student{
    int id // simple example
    };
    main(){
    modify_data(); // calls the function.
    }
    lode_struct_function()
    {
    // here I load the struct value from the file.
    struct student line[i] // i comes from another function.
    line[i].id = student_id;
    }
    modify_data()
    {
    struct student line[i]  // ? ?????
    printf("%d",line[i].id); // here is the key how can i print line[i].id on this function?
    }
    Last edited by programinproces; 10-31-2013 at 01:35 AM.

  2. #2
    C++ Witch laserlight's Avatar
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    Make use of a pointer, e.g.,
    Code:
    #include <stdio.h>
    
    struct student
    {
        int id;
    };
    
    void modify_data(struct student *the_student)
    {
        the_student->id = 1;
    }
    
    int main(void)
    {
        struct student a_student = {0};
        modify_data(&a_student);
        /* print the struct, etc */
        return 0;
    }
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  3. #3
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    Thanks. But I have another function witch loads the struct value from the line of text file.
    Code:
    int load_struct()                                        //this function loads structs element from the file.{
        int x=0;
        int i=count(x);
        struct student line[i];
        char file_line[100];
        char* line_parts;
        
        FILE * fp;                                                          // file opens here.
        if ((fp = fopen ("file.txt", "r")) != NULL)
        {
            while (x<i) {
                fgets(file_line,100,fp);     // gets line from the file.
                
                
                line_parts = strtok(file_line,",");
                line[x].st_id  = atoi(line_parts);
                
                
                line_parts = strtok(NULL, ",");
                strcpy(line[x].st_name,line_parts);
                
                line_parts = strtok(NULL, ",");
                line[x].st_age = atoi(line_parts);
                
                line_parts = strtok(NULL, ",");
                strcpy(line[x].st_dep,line_parts);
                
                line_parts = strtok(NULL, ",");
                line[x].st_grade = atoi(line_parts);
                x++;
                
            }
            
            
        }
        fclose(fp);
    
    
        return  0;
    }
    Now I have to use these value in modify_data function. I only call load_struct and modify_data function in the main?
    Sorry I am new and not doing much in the pointer. Thanks again.

  4. #4
    SAMARAS std10093's Avatar
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    Notice that you store the data of the file in an array of structs, which is locally declared, thus will go out of scope when the function terminates.

    I think an example like this is what you need to get you boosted.
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  5. #5
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    SO, if I declare this line as a global variable does that work?
    struct student line[i];
    this way.
    Code:
    struct student{
       int id;
    }line[i]; // to do this way i am getting complain about [i].
    Last edited by programinproces; 10-31-2013 at 03:54 PM.

  6. #6
    and the Hat of Guessing tabstop's Avatar
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    Are you wanting the function to fill in the whole array, or just one single item/struct/object in that array?

    In either case the array should exist in the calling function, not the called function, and certainly not globally; and you should pass the relevant thing into your function. (If you just want to fill in a single object, you would maybe need to pass-by-address so that the contents can be modified.)

  7. #7
    11DE784A SirPrattlepod's Avatar
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    Quote Originally Posted by tabstop View Post
    Are you wanting the function to fill in the whole array, or just one single item/struct/object in that array?

    In either case the array should exist in the calling function, not the called function, and certainly not globally; and you should pass the relevant thing into your function. (If you just want to fill in a single object, you would maybe need to pass-by-address so that the contents can be modified.)
    Yikes. I know it's probably a typo or simplification but there is no such thing as "pass-by-address" in C. I'd modify the statement to read "If you just want to fill in a single object, you would maybe need to a pointer to the object so that the contents can be modified."

  8. #8
    and the Hat of Guessing tabstop's Avatar
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    Quote Originally Posted by SirPrattlepod View Post
    Yikes. I know it's probably a typo or simplification but there is no such thing as "pass-by-address" in C. I'd modify the statement to read "If you just want to fill in a single object, you would maybe need to a pointer to the object so that the contents can be modified."
    "Pass the address"? "Pass-by-pointer"? You can pick whichever you like. (I think "pass-by-pointer" is probably most common, though? And the CS people probably like "pass by reference", although then you can get into an argument with the C++ people.)

  9. #9
    11DE784A SirPrattlepod's Avatar
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    Quote Originally Posted by tabstop View Post
    "Pass the address"? "Pass-by-pointer"? You can pick whichever you like. (I think "pass-by-pointer" is probably most common, though? And the CS people probably like "pass by reference", although then you can get into an argument with the C++ people.)
    But in C everything is pass-by-value.

  10. #10
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    Thanks all for your valuable suggestion, Now I'm getting little higher in the pointer. Can you please, suggest me for my illusion about the pointer?
    lets say, I have function called fn1(), fn2() and fn3(). I need to do this.
    Code:
    fn1()
    {
    fn2() // simply i call fn2() here
    fn3(*fn2()) // is that it pass by reference ?????
    }
    fn2()
    {
    //something and something
    }
    fn3(what i put here?)
    {
    //something or manything 
    }
    is that possible to do ?
    Last edited by programinproces; 11-01-2013 at 02:32 PM.

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