Saving text out of a struct in a char array

Question

I have a struct with letters inside and I want to give the letters to an array so i can use it afterwards. It works if i would just print the letters.

Top (struct):

 #include "stdafx.h"

typedef struct { char* code; char* letter;}morse_tabelle; 

morse_tabelle tabelle[] = {
    { ".-", "A" },
    { "-...", "B" },
    { " -.-. ", "C" },
    { "-..", "D" },
    { ".", "E" },
    { "..-.", "F" },
    { "--.", "G" },
    { "....", "H" },
    { "..", "I" },
    { ".---", "J" },
    { "-.-", "K" },
    { ".-..", "L" },
    { "--", "M" },
    { "-.", "N" },
    { "---", "O" },
    { ".--.", "P" },
    { "--.-", "Q" },
    { ".-.", "R" },
    { "...", "S" },
    { "-", "T" },
    { "..-", "U" },
    { "...-", "V" },
    { ".--", "W" },
    { "-..-", "X" },
    { "-.--", "Y" },
    { "--..", "Z" },
    { "-----", "0" },
    { ".----", "1" },
    { "..---", "2" },
    { "...--", "3" },
    { "....-", "4" },
    { ".....", "5" },
    { "-....", "6" },
    { "--...", "7" },
    { "---..", "8" },
    {"----.", "9" },
    { "/", " " },
    };

For the arraysize:

#define ARR_SIZE(x) (sizeof(x)/sizeof((x)[0]))

Function:

    void morse_to_text(void)
    {


    char input[100];
    char* morse_letter;

    int j = 0;
    char* translation[50];


    printf_s("\n\nput in Morsecode:\n\n");
    fgets(input, 100, stdin);                                             
    input[strlen(input)-1] = '\0';                                       

    morse_letter = strtok(input, " ");                               

    while (morse_letter)                                                      
    {
        for (int i = 0; i < ARR_SIZE(tabelle); i++)                            
        {

            if (!strcmp(morse_letter, tabelle[i].code))                  
            {
                translation[j] = tabelle[i].letter;                    
                j++;
                /*printf_s("%s", tabelle[i].letter);*/   //This works              
            }
        }
        morse_letter = strtok(NULL, " ");                            
    }

    /*output*/
    printf_s("\n\n---------------\n\n");
    for (int i = 0; i <= strlen(translation[50]); i++){
            printf("%s", translation[i]);
    }

};

It sort of works if i change the char* letter to char letter inside of the struct. but then i get a buffer overrun. The question again: how can i store strings inside an array.

for (int i = 0; i <= strlen(translation[50]); i++) -> for (int i = 0; i < j; i++) — Jabberwocky
– Jabberwocky, Commented May 3, 2017 at 8:50

Aconcagua · Accepted Answer · 2017-05-03 08:59:45Z

3

What you actually want is this:

char translation[50]; // no string array, char array!

Then have the letter as char as you intended:

typedef struct { char* code; char letter;} morse_tabelle;

With that, you now can simply do

translation[j] = tabelle[i].letter;

again, just as before. Only the data type changed...

However, you need to null-terminate your translated string, else you cannot use it with printf("%s", translation)

while(...) { ... }
translation[j] = 0;

// output:
// no for loop any more!

printf("%s", translation);

An alternative to terminating the null character would be giving the length to the printf format parameter:

while(...) { ... }
// no termination any more...

// output:
// no for loop any more!

printf("%.*s", j, translation);

See printf for details (OK, link actually is C++, but documentation is exactly true for C, too...).

answered May 3, 2017 at 8:59

Aconcagua

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2 Comments

AlastairG Over a year ago

Same answer as mine but slightly better laid out and includes detail of null termination which I missed since I took it for granted.

krausl Over a year ago

i tried it similar before, the biggest problem was that i didnt terminate the translation-array with a 0, so i got a bufferoverload i guess. now with this it works well

AlastairG · Accepted Answer · 2017-05-04 13:25:03Z

1

Instead of:

translation[j] = tabelle[i].letter;

do:

translation[j] = tabelle[i].letter[0];

Or instead, and even better, do:

typedef struct { char* code; char letter;} morse_tabelle; 

morse_tabelle tabelle[] = {
    { ".-", 'A' },
    { "-...", 'B' },
    { " -.-. ", 'C' },
    { "-..", 'D' },
    etc. etc.

char translation[50];
...
printf("%s\n", translation);

Or, if you want to print out the translation letter by letter:

for (int i = 0; i < strlen(translation); i++)
{
    printf("%c\n", translation[i]);
}

To add some basic C tuition:

char * is a pointer to an array of char types. "A" is a char array with two elements and can be written as { 'A', '\0' }. Hence assigning "A" to a char type is wrong.

If you define letter as a char * and populate the data with a one character string, then you can access the character by indexing the 0th element as letter[0]. However, rather than using character arrays all over the space and wasting memory and over-complicating your code, it is better just to use characters instead.

edited May 4, 2017 at 13:25

answered May 3, 2017 at 8:47

AlastairG

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4 Comments

Jabberwocky Over a year ago

This answer is not quite correct. Rethink it please.

AlastairG Over a year ago

It would be nice if you would point out exactly which part of this answer is not correct. In truth the original code is so full of bugs that it needs a complete rewrite for a fully correct answer and I don't have time for that.

Jabberwocky Over a year ago

You write Instead of: translation[j] = tabelle[i].letter; do: translation[j] = tabelle[i].letter[0];, but this implies that you need also modify what you have described under Or, even better do:.

AlastairG Over a year ago

@Michael Walz, thanks. It was correct, just a question of unclear text. There was an implicit "instead" in the second option that I have now made explicit.

Jabberwocky · Accepted Answer · 2017-05-03 08:59:15Z

0

Here:

for (int i = 0; i <= strlen(translation[50]); i++) {

strlen(translation[50] is wrong. translation is an array of 50 pointers to char*. So strlen(translation[50]) is the length of the 50th translated character (which BTW only exists if you have typed in 50 morse codes) and not the number of elements you've put into the translation array. You've put j char* pointers into the translation array, therefore the correct code is:

for (int i = 0; i < j); i++) {

answered May 3, 2017 at 8:59

Jabberwocky

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3 Comments

n.caillou Over a year ago

translation[50] actually asks for the 51th element

Jabberwocky Over a year ago

@n.caillou yes if you start at 1.

krausl Over a year ago

this was a good example for me to understand pointers a bit more, thank you.

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