Converting an int into a 4 byte char array (C)

user_154619 0
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Hey, I'm looking to convert a int that is inputed by the user into 4 bytes, that I am assigning to a character array. How can this be done?

Example:

Convert a user inputs of 175 to

00000000 00000000 00000000 10101111

Issue with all of the answers so far, converting 255 should result in 0 0 0 ff although it prints out as: 0 0 0 ffffffff

unsigned int value = 255;   

buffer[0] = (value >> 24) & 0xFF;
buffer[1] = (value >> 16) & 0xFF;
buffer[2] = (value >> 8) & 0xFF;
buffer[3] = value & 0xFF;

union {
    unsigned int integer;
    unsigned char byte[4];
} temp32bitint;

temp32bitint.integer = value;
buffer[8] = temp32bitint.byte[3];
buffer[9] = temp32bitint.byte[2];
buffer[10] = temp32bitint.byte[1];
buffer[11] = temp32bitint.byte[0];

both result in 0 0 0 ffffffff instead of 0 0 0 ff

Just another example is 175 as the input prints out as 0, 0, 0, ffffffaf when it should just be 0, 0, 0, af

c
10 Answers

An int is equivalent to uint32_t and char to uint8_t.

I'll show how I resolved client-server communication, sending the actual time (4 bytes, formatted in Unix epoch) in a 1-bit array, and then re-built it in the other side. (Note: the protocol was to send 1024 bytes)

  • Client side

    uint8_t message[1024];
uint32_t t = time(NULL);

uint8_t watch[4] = { t & 255, (t >> 8) & 255, (t >> 16) & 255, (t >> 
24) & 255 };

message[0] = watch[0];
message[1] = watch[1];
message[2] = watch[2];
message[3] = watch[3];
send(socket, message, 1024, 0);

  • Server side

    uint8_t res[1024];
uint32_t date;

recv(socket, res, 1024, 0);

date = res[0] + (res[1] << 8) + (res[2] << 16) + (res[3] << 24);

printf("Received message from client %d sent at %d\n", socket, date);

Hope it helps.

user_79225110

You can simply use memcpy as follows:

unsigned int value = 255;
char bytes[4] = {0, 0, 0, 0};
memcpy(bytes, &value, 4);
user_106868900
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