Array of "strings" in C

Question

I know that there is a question with the same name, but it didn't work for me. I'm making a home-compiler, returns the words that belongs to a language.

The words to analyze are in this vector:

char *cadenas[]= {"123", "4567L", "5a23", '\0'};

Now I want to enter the words by console, but strings can't be used in C, how can I do it? (Without making a matrix possibly)

void getCadenas(char *cadenas[]){

    printf("Enter cadenas to be analyzed ('z' to scape) \n \n");

    char cadena[15];
    gets(cadena);
    int x=0;

    while(cadena[0]!='z'){
        strcpy(cadenas[x],cadena);
        x++;
        gets(cadena);
    }
}

Your `cadenas` is basically is _sort-of_ a matrix already (array of an array). So what is the question? — KovBal, Aug 05 '15 at 22:20
Strings can't be used? Strings can be used. Question could do with a tidy-up, unclear what you want. — Veltas, Aug 05 '15 at 22:21
Did you look at [Taking user input and storing it in an array of strings in C](http://stackoverflow.com/q/30428615/3466415)? Does it solve your problem? If not, why not? — David K, Aug 05 '15 at 22:23
`strcpy(cadenas[x],cadena);` : Rewriting of the string literal is not allowed. (Also it does not have enough space.) — BLUEPIXY, Aug 05 '15 at 22:35
also, you probably want to use `strncopy(destination, src, length)` to make sure you don't walk off the location you're copying to... — Purag, Aug 05 '15 at 22:38
Note: I'd expect `{"123", "4567L", "5a23", NULL}` rather than `{"123", "4567L", "5a23", '\0'}` — chux - Reinstate Monica, Aug 05 '15 at 22:47
@chux i think he probably is looking for a null terminated empty string as the last entry in his array of strings, which isn't NULL — Neil, Aug 05 '15 at 22:55
never **ever** use `gets()`, it's [broken](http://man7.org/linux/man-pages/man3/gets.3.html#BUGS) — , Aug 05 '15 at 22:57
@Neil: it's an array of pointers, `NULL` is appropriate, `'\0'` is not — Veltas, Aug 05 '15 at 22:59
@Veltas hmm I didn't say he had it correct - but I would not be passing NULL into strcpy without first checking as this is going to lead to an exception.. — Neil, Aug 05 '15 at 23:08

Pynchia · Answer 1 · 2015-08-06T00:55:18.960

If I understand your problem correctly, you would like the user to be able to enter multiple strings, until he/she types z

See if this piece of code helps you out. The strings will be stored in the cadenas array, as requested.

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

#define MAX_CADENAS 100
#define MAX_CADENA_LEN 255
int getCadenas(char **cadenas){
    int x=0;
    char cad[MAX_CADENA_LEN+1];
    printf("Enter cadenas to be analyzed ('z' to scape) \n \n");

    while(x<MAX_CADENAS) {
        scanf("%s", cad);
        if (strcmp(cad,"z")==0)
            break;
        cadenas[x] = malloc(strlen(cad)+1);
        strcpy(cadenas[x], cad);
        x++;
    }
    return x;
}

char *cadenas[MAX_CADENAS];
int main() {
    int num, i;

    num = getCadenas(cadenas);
    for (i=0;i<num; i++) {
        printf("%s\n", cadenas[i]);
    }
}

Note0: the code assumes you know in advance what the maximum number of input strings can be (100). It also assumes a maximum size for each input string (255 characters)

Note1: gets is deprecated. Also, instead of scanf, you might want to use fgets.

Note2: the present code is for illustrative purpose only. It allocates memory for each input string, but it assumes no error occurs in doing so (i.e. it does not check what malloc returns).

Note3: the allocated memory blocks must be freed when not used anymore (hint: cycle through the cadenas array and use free)

You should probably just change your answer to use fgets, given that it's not hard to use and is about as long as a scanf call anyway. — Veltas, Aug 06 '15 at 10:36

Veltas · Answer 2 · 2018-06-16T12:39:41.343

Assuming you don't mind carrying on with fixed-size strings and arrays, here is your original program modified:

#include <stdio.h>
#include <string.h>
#define MAX_CADENAS 100
#define CADENA_LIMIT 1000

// ...

void getCadenas(char cadenas[MAX_CADENAS][CADENA_LIMIT]){

    printf("Enter cadenas to be analyzed ('z' to scape) \n \n");

    int x;
    for(x=0; x<MAX_CADENAS-1; x++){
        char cadena[CADENA_LIMIT];
        fgets(cadena, CADENA_LIMIT, stdin);
        // fgets will copy the newline character, we don't want that
        int cadenaLength=strlen(cadena);
        if(cadena[cadenaLength-1]=='\n')
            cadena[cadenaLength-1]='\0';
        if(strcmp(cadena, "z")==0) break;
        strcpy(cadenas[x], cadena);
    }
    cadenas[x][0]='\0';
}

// ...

Prefer fgets as you can prevent overflow of the fixed-size strings. Unfortunately it copies the newline as well, so I have code to handle that. The result is an array in the form you originally specified (except it ends with "" which we decided was what you were after in the comments).

You can read arbitrary sized strings in C like in other languages, but you would need to implement it with malloc() and co. Allocating dynamically sized memory is primarily controlled with the functions malloc, calloc, realloc and free. This would make the program unavoidably more complicated. Here is one way of doing this:

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

// ...

char *getCadena(){
    int length=0, capacity=1, character;
    char *cadena=malloc(1); // sizeof(char) is always 1
    while((character=getchar())!=EOF){
        if(character=='\n') break;
        // Add character to string
        length++;
        if(capacity<length){
            capacity*=2;
            cadena=realloc(cadena,capacity);
        }
        cadena[length-1]=character;
    }

    // Add terminator to cadena
    length++;
    if(capacity<length){
        capacity*=2;
        cadena=realloc(cadena,capacity);
    }
    cadena[length-1]='\0';

    return cadena;
}

char **getCadenas(){

    printf("Enter cadenas to be analyzed ('z' to scape) \n \n");

    int length=0, capacity=1;
    char **cadenas=malloc(sizeof(char *));
    for(;;){
        char *cadena=getCadena();
        if(strcmp(cadena,"z")==0){
            free(cadena);
            break;
        }
        // Add pointer to cadenas array
        length++;
        if(capacity<length){
            capacity*=2;
            cadenas=realloc(cadenas,capacity*sizeof(char *));
        }
        cadenas[length-1]=cadena;
    }

    // Add NULL to end of cadenas
    length++;
    if(capacity<length){
        capacity*=2;
        cadenas=realloc(cadenas,capacity*sizeof(char *));
    }
    cadenas[length-1]=NULL;

    return cadenas;
}

void freeCadenas(char **cadenas){
    int i=0;
    while(cadenas[i]!=NULL){
        free(cadenas[i]);
        i++;
    }
    free(cadenas);
}

// ...

This works mostly the same as the previous function, except you should use freeCadenas eventually, and I end the array with NULL instead of "" which is customary.

The code is a lot longer, but it's pretty typical of more sophisticated C code with less arbitrary limits. In fact real C code usually has more robust handling of errors and more generic functions for managing dynamic arrays. If you actually manage to make this "home-compiler", however, you will figure all this out for yourself.

Array of "strings" in C

2 Answers2