如何在C语言中将char *复制到char *数组

Question

I am trying to generate uint_32 random numbers which should be stored in the buffer array, but somehow, my codes only stores last value every time.

For instance, when I generate random numbers like

12365645
97897875
45458788

then the value of

buffer[0]=12365645
buffer[1]=97897875
buffer[2]=45458788

However currently, I am getting like

buffer[0]=45458788
buffer[1]=45458788
buffer[2]=45458788

Here is my corresponding code but ain't sure where I have made a mistake.

/*Required header files are added*/
#include <stdio.h>
#include <pthread.h>
#include <stdlib.h>
#include <unistd.h>         
#include <fcntl.h>
#include <stdint.h>

struct thread_arguments
{
    char *buffer;
    char *queue[10];
    uint32_t offset;
    uint32_t r;
    size_t bufferlen;


    size_t minlevel;


}ta;

void randomgenerate();
void constructor(int size, int filllevel);
void put_buffer(int ele);

void printbuf();
int main(void)
{
ta.offset=0;
ta.buffer=NULL;

    constructor(1,3);
    randomgenerate();
    printbuf();

    return EXIT_SUCCESS;

}
void constructor( int filllevel,int size)
{   
    //ta.buffer[size];
     ta.bufferlen=size;  
     ta.minlevel=filllevel;
}

void randomgenerate()
{
int i;
    for(i=0;i<ta.bufferlen;i++)
    {
                int myFile = open("/dev/random", O_RDONLY);             
                read(myFile, &ta.r, sizeof(ta.r)) ;

                put_buffer(i);
                close(myFile);

    }
}
void put_buffer(int ele)
{


ta.buffer = realloc(ta.buffer, sizeof(uint32_t));
sprintf(ta.buffer, "%zu", ta.r);
ta.offset += sizeof(uint32_t);
ta.queue[ele]=ta.buffer;
printf("%d\t%s\n",ele,ta.queue[ele]);

}
void printbuf()
{
int k;

    for(k=0;k<ta.bufferlen;k++)
    {
    printf("%s\n",ta.queue[k]);
    }
}

Answer 1

You're misusing realloc() . Your ta.buffer is always pointing to the same ta.buffer because it's already equal to sizeof (uint32_t) . So when you do the assignment ta.queue[ele] = ta.buffer , every ta.queue pointer is the same value.

What you need is malloc() .

EDIT

You should be using malloc() for each call to put_buffer() , like this:

void put_buffer (int ele)
{
    /* There are 10 decimal digits (characters) in a 32-bit unsigned integer, + 1 for the null terminator */
    ta.buffer = malloc ((sizeof *ta.buffer) * 11); 
    /* Print the string representation to the newly-allocated buffer */
    sprintf(ta.buffer, "%u", ta.r);
    /* I'm not sure what this is for so I'll leave it alone */
    ta.offset += sizeof (uint32_t);
    ta.queue[ele] = ta.buffer;
}

Answer 2

Not only are you using realloc with the same size every time, the amount of memory you are allocating is not right.

 ta.buffer = realloc(ta.buffer, sizeof(uint32_t));
 sprintf(ta.buffer, "%zu", ta.r);

sizeof(uint32_t) will be 4 . That is not enough memory to store an object of type uint32_t in string form.

Your program is subject to undefined behavior.