Thread: Writing and Reading unit32_t values using htons and ntohs

Hey there,

I'm having an issue with writing uint32_t values to file and then reading them back.

Code:

//My code to write the value is as follows,

//eklen = 128

FILE* pFilOutput = open_memstream(pChrOutputBuffer, &pSizTotalSize);
uint32_t eklen_n = htonl(eklen);
if (fwrite(&eklen_n, sizeof(uint32_t), 1, pFilOutput) != 1) {
   //Failed to write data
}

//My code to read the value back again is as follows,

FILE* pFilInput = fmemopen(pChrData, strlen(pChrData), "r");
uint32_t eklen_n;
fread(&eklen_n, sizeof(eklen_n), 1, pFilInput);
int eklen = ntohl(eklen_n);

Wrote = -2147483648
Read 1344601458

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I'm guessing I'm making a school boy error here but I just can't see it. I thought maybe I needed to specify "b" in the fmemopen mode parameter but that didn't help and on further reading I assume it's binary by default anyway.

Any ideas what I'm doing wrong? Many thanks in advance for any help!

Nick.

Are you checking your fread() call for success?

This doesn't look like a problem with htonl/ntohl, since the values aren't the byte-reversed values of one another.

Originally Posted by JohnGraham

Are you checking your fread() call for success?

This doesn't look like a problem with htonl/ntohl, since the values aren't the byte-reversed values of one another.

Hey John, yup, I've added checks for that and it's returning without error.