recv() C error invalid conversion from char to int

Question

I have some C code below:

char update[MAX_UPDATE_LEN];
int remoteLen;

char pholder;
pholder = recv(update,connectDescriptor,MAX_UPDATE_LEN,MSG_DONTWAIT); //error
remoteLen = atoi("pholder");

I keep getting the following errors:

client.cpp:849: error: invalid conversion from `char*' to `int'

client.cpp:849: error: initializing argument 1 of `ssize_t recv(int, void*, 
size_t, int)'

client.cpp:849: error: invalid conversion from `int' to `void*'

client.cpp:849: error: initializing argument 2 of `ssize_t recv(int, void*, 
size_t, int)'

What is causing these errors?

Answer 1

There are several issues with this code:

char update[MAX_UPDATE_LEN];
int remoteLen;

char pholder;
pholder = recv(update,connectDescriptor,MAX_UPDATE_LEN,MSG_DONTWAIT); <-- error here
remoteLen = atoi("pholder");

1. recv returns an ssize_t which is usually much bigger than a char . So you can't safely store the return code in pholder .
2. The arguments to recv() are in the wrong order. Here's the declaration: ssize_t recv(int sockfd, void *buf, size_t len, int flags);
3. atoi is being passed a string which is not a number "pholder" . It expects a string like "12345" . If ASCII-encoded numerals is what you expect, you can give update to atoi .

Bonus: use sizeof(update) instead of MAX_UPDATE_LEN for len -- that way if the type declaration or size of update changes, you should still get the expected value.

Here's how you might fix it:

char update[MAX_UPDATE_LEN];

const int flags = MSG_DONTWAIT;
const ssize_t ret = recv(connectDescriptor, update , sizeof(update), flags);
if (-1 == ret)
{
    perror("recv");
    exit(1);
}
const int remoteLen = strtol(update, update + sizeof(update), 0);