Question

I need to get a string without asking for a length,
I create a buffer of 100 char and when is full I do a realloc to add a space for a char at the end of the string

this is my code…could you help me?

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

int main(int argc, char **argv)
{   
    char *content = malloc(10*sizeof(char));
    char c;
    content[0]='\0';

    while ((c = getchar()) != EOF)
    {
        if (strlen(content) < 10){
            strcat(content, &c);
            content[strlen(content)+1] = '\0';
        }
       else {
            content=realloc(content,sizeof(char)*(strlen(content))+2);
            strcat(content, &c);
            content[strlen(content)+1] = '\0';
        }
    }
    printf("%s",content);       

    return 0;
}

Answer 1

A few issues here:

1. don’t use strcat like that! You should pass a pointer to a \0 terminated string, instead of a pointer to a single char. This only works by accident.
2. Keep track of the allocated memory size in a separate variable, instead of using strlen().
3. Keep track of the position in the string using another separate variable, not by calling strlen() constantly. Set the terminating \0 once, after the loop is done.
4. a better reallocation strategy would be to grow memory allocation in chunks, i.e. not for every byte. You could allocate X bytes every time your allocated memory is exhausted, or you could double the number of allocated bytes.