simple use of malloc and realloc

Hi guys i want to improve my knowledge about the dyn allocation of char pointers... with this code i wanted to type a string and insert the string in a array created dynamically:

Code:

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


int main()
{


char c;
char *test=NULL;
unsigned int len;


test = (char*) malloc (sizeof(char));
printf("Gimme a string: ");
while(c != '\n'){


            scanf("%c", &c);
            test = realloc (test, sizeof(char));
            len = strlen(test);
            test[len]=c;
            test[len+1]='\0';
}


printf("\nThis is the dynamic string: %s", test);


printf("\n\n");
system("PAUSE");
return 0;
}

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That crew this output:

Quote:

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Gimme a string: Hello World

This is the dynamic string: °):Hello World

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and i don't understand why there are these 3 initial character '°' ')' ':' that i didn't have typed...

test = realloc (test, sizeof(char));

You allocate ONLY a single char then you over-write your program stack; you are lucky your program ran without crashing.

I suggest re-reading the docs realloc - C++ Reference

You have a single byte (char) allocated then you tell realloc to change it to a single byte once more. It does NOT add a byte.

Tim S.

i want to allocate a single char for each cicle and for each char.. one by one... can you explain me the correct way to do this operation in a right way?

Quote:

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Originally Posted by zmone

i want to allocate a single char for each cicle and for each char.. one by one...

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You didn't initialize len or c, which is a problem. Helpful is to see that if you allocate len bytes, the index len-1 is always the last index. Try the following

Code:

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char c='\0';
char *test=NULL;
unsigned int len=1; // initial size is 1 byte

test = (char*) malloc (len*sizeof(char));
test[len-1] = '\0';
printf("Gimme a string: ");

while(c != '\n'){
            scanf("%c", &c);
            test[len-1]=c;
            len++;
            test = realloc (test, len*sizeof(char));
            test[len-1]='\0';
}

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Quote:

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Originally Posted by zmone

i want to allocate a single char for each cicle and for each char.. one by one... can you explain me the correct way to do this operation in a right way?

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Read and learn; if you do not understand ask smart questions.
realloc - C++ Reference