Question

the error generate is : Segmentation fault

Myheader.h

#ifndef datest
#define datest
struct date{
    char c;
    FILE* gestor;
};

typedef struct date dateStruct;
extern dateStruct date_Struct;

void loadLine();
#endif

myMain.c

#include "myheader.h"
...

dateStruct date_Struct;

int main(int argc,char* argv[]){
        date_Struct.gestor = fopen(argv[1],"r");
        loadLine();
}

MyHeader.c

#include "myheader.h"

void loadLine(){
    char* TEXT;
    fscanf(date_Struct.gestor, "%s\n", TEXT);  //ERROR! why?
    ...

}

I can’t solve this , i need declare the extern var in myheader.c too?

Answer 1

The segmentation fault might occur because the file wasn’t opened successfully and date_Struct.gestor is a NULL pointer.

Check the return value from fopen() — always! It may fail, and if you use the null pointer, you get segmentation faults.

The other problem is with TEXT (don’t use all-caps for variables; use lower-case or camel-case and reserve all-caps for macros).

The pointer TEXT does not point anywhere; it is not initialized. When you read using it, all hell breaks loose. (The pointer might point anywhere; in the worst case scenario, it points to somewhere valid but unexpected, your fscanf() ‘works’, but you trample over some data and you’ve no idea how it got corrupted. A segmentation fault is fortunate; it tells you that something was clearly wrong.) This is more plausibly your problem.

void loadLine()
{
     char TEXT[4096];
     if (fscanf(date_Struct.gestore, "%s\n", TEXT) != 1)
         ...process error...

Check the return value from fscanf() too; it tells you whether it worked as you expected or not. Get used to checking for error returns. It’s always necessary to know how to handle errors, and quite a lot of code is usually devoted to doing so.