Memory limit exceeded in C

Question

I'm currently being a tutor for a student in C. For his classes, the university has installed a server running Mooshak (software capable of receiving code and test it).

We have developed code, compiled it and tested it locally before sending to the server and everything went fine. However, when we tried to send it to the server, the server stated "Memory Limit Exceeded".

The code looked as follows:

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

#define LIMITE_CARACTERES 1000
#define LIMITE_GENES 100000

char genes[LIMITE_GENES][LIMITE_CARACTERES];

char* copiar_por_espaco(char* string, char* dest)
{
    for(int i = 0; i < strlen(string); i++)
    {
        if(' ' == string[i])
        {
            strncpy(dest, string, i);
            dest[i] ='\0';
            if( i + 1 >= strlen(string))
                return NULL;
            else
                return &string[i+1];
        }
    }
    if(strlen(string) == 0)
    {
        return NULL;
    }
    else
    {
        strcpy(dest, string);
        return NULL;
    }
}


void genes_f()
{
    char s[LIMITE_CARACTERES];
    int numero_genes = 0;
    while(scanf("%s", s) != EOF)
    {
        char *auxiliar = s;
        while(auxiliar != NULL && strlen(auxiliar) != 0)
        {
            auxiliar = copiar_por_espaco(auxiliar, genes[numero_genes]);
            numero_genes++;
        }
    }
    if(numero_genes <= 20)
    {
        for(int i = 0; i < numero_genes; i++)
        {
            printf("%s\n", genes[i]);
        }
    }
    else
    {
        for(int i = 0; i < 10; i++)
        {
            printf("%s\n", genes[i]);
        }

        for(int i = numero_genes - 10; i < numero_genes;i++)
        {
            printf("%s\n", genes[i]);
        }
    }
}


int main()
{
    genes_f();
    return 0;
}

Please note that the values LIMITE_CARACTERES and LIMITE_GENES are an assignment requirement (they haven't been told about memory allocation yet). The above code gives the "Memory Limit Exceeded", but if I split the first four into two lines, the server does not throw that error and accepts our solution:

char* copiar_por_espaco(char* string, char* dest)
{
    int len = strlen(string); // This line was taken out from the for
    for(int i = 0; i < len; i++) // Now we used the variable instead
    {
        if(' ' == string[i])
        {
            strncpy(dest, string, i);
            dest[i] ='\0';
            if( i + 1 >= strlen(string))
                return NULL;
            else
                return &string[i+1];
        }
    }
    if(strlen(string) == 0)
    {
        return NULL;
    }
    else
    {
        strcpy(dest, string);
        return NULL;
    }
}

I have no idea why. Is there an explanation for this?

The input will several lines with words (blank lines should be skipped), separated by a space. The program should separate and take each word:

Input

A BDD TES QURJ

test dog cat heart

cow
bird tree

Output

A
BDD
TES
QURJ
test
dog
cat
heart
cow
bird
tree

Answer 1

You forgot to include an extra byte for null terminators in your array. If LIMITE_CARACTERES is the maximum length of a string provided as input, then you need an array of size LIMITE_CARACTERES + 1 in which to store it. So you need to change this line

char genes[LIMITE_GENES][LIMITE_CARACTERES];

to

char genes[LIMITE_GENES][LIMITE_CARACTERES + 1];

Answer 2

Since you are a tutor, I give feedback so you can properly teach your student (so this is not an answer to your problem).

copiar_por_espaco

for(int i = 0; i < strlen(string); i++)

Repeatedly calling strlen on a variable that does not change in the loop is a waste of CPU cycles. Indeed, you should calculate the length before the loop and use it in the loop. That also holds for if( i + 1 >= strlen(string))

if(' ' == string[i])...

Note that it is guaranteed the string does not hold spaces because it was read with scanf. As a consequence, the function will always return NULL.

if(strlen(string) == 0) return NULL;

You test this after the loop but logic dictates you do this before any processing and it could be shortened to if (!*string) return NULL; This would also make the code more beautiful as the else part is not needed (it is not needed anyway).

genes_f

while(scanf("%s", s) != EOF)

A scanf-guru might help here but I believe there must be a space in the format specifier so it will skip leading spaces, " %s". I believe your way will read only one string and then will loop indefinitely returning zero on each scanf call. You should test the result of scanf for the number of format specifiers successfully converted and not for EOF. So check for 1.

if(numero_genes <= 20)

Your printing is funny. It all can be as one loop:

    for(int i = numero_genes; i < numero_genes; i++)
        printf("%s\n", genes[i]);

You have to do bounds checks on your number of genes:

numero_genes<LIMITE_GENES