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cbufferlow-level-code

What does this syntax *((unsigned int *)(buffer+i)) mean in C

This is the code:

char *command, *buffer;

command = (char *) malloc(200);
bzero(command, 200);

strcpy(command, "./notesearch \'");
buffer = command + strlen(command);
for(int i=0; i < 160; i+=4) {
    *((unsigned int *)(buffer+i)) = ret; // What does this syntax mean?
}

You can get the full code here => https://raw.githubusercontent.com/intere/hacking/master/booksrc/exploit_notesearch.c

Please help me I'm a beginner.

Solution

  • Read it from the inner part to the outer. Here we must suppose that buffer is a pointer to some memory area or array element. You have:

    • buffer + 1 ==> address to next memory position or next array element
    • (unsigned int *)(buffer+i) ==> cast of resulting pointer to a pointer of type unsigned int.
    • *((unsigned int *)(buffer+i)) ==> dereference the unsigned int pointed out (get the value).
    • *((unsigned int *)(buffer+i)) = ret; ==> assign the value to the variable ret.

    In C, when evaluating expressions, always go from the inside to the outer.