No warning from gcc when function definition in linked source different from function prototype in h
- by c_c
Hi,
I had a problem with a part of my code, which after some iterations seemed to read NaN as value of a int of a struct. I think I found the error, but am still wondering why gcc (version 3.2.3 on a embedded Linux with busybox) did not warn me. Here are the important parts of the code:
A c file and its header for functions to acquire data over USB:
// usb_control.h
typedef struct{
double mean;
short *values;
} DATA_POINTS;
typedef struct{
int size;
DATA_POINTS *channel1;
//....7 more channels
} DATA_STRUCT;
DATA_STRUCT *create_data_struct(int N); // N values per channel
int free_data_struct(DATA_STRUCT *data);
int aqcu_data(DATA_STRUCT *data, int N);
A c and header file with helper function (math, bitshift,etc...):
// helper.h
int mean(DATA_STRUCT *data);
// helper.c (this is where the error is obviously)
double mean(DATA_STRUCT *data)
{
// sum in for loop
data->channel1->mean = sum/data->N;
// ...7 more channels
// a printf here displayed the mean values corretly
}
The main file
// main.c
#include "helper.h"
#include "usb_control.h"
// Allocate space for data struct
DATA_STRUCT *data = create_data_struct(N);
// get data for different delays
for (delay = 0; delay < 500; delay += pw){
acqu_data(data, N);
mean(data);
// printf of the mean values first is correct. Than after 5 iterations
// it is always NaN for channel1. The other channels are displayed correctly;
}
There were no segfaults nor any other missbehavior, just the NaN for channel1 in the main file.
After finding the error, which was not easy, it was of course east to fix. The return type of mean(){} was wrong in the definition. Instead of double mean() it has to be int mean() as the prototype defines. When all the functions are put into one file, gcc warns me that there is a redefinition of the function mean(). But as I compile each c file seperately and link them afterwards gcc seems to miss that.
So my questions would be. Why didn't I get any warnings, even non with gcc -Wall? Or is there still another error hidden which is just not causing problems now?
Regards,
christian
