Question

For those experienced with C, this will be a simple memory allocation/referencing problem:

Here are my data structures:

struct configsection {
    char *name;
    unsigned int numopts;
    configoption *options;
};
typedef struct configsection configsection;

struct configfile {
    unsigned int numsections;
    configsection *sections;
};
typedef struct configfile configfile;

Here are my routines for initializing a configsection or configfile, and for adding a configsection to a configfile:

// Initialize a configfile structure (0 sections)
void init_file(configfile *cf) {
    cf = malloc(sizeof(configfile));
    cf->numsections = 0;
}
// Initialize a configsection structure with a name (and 0 options)
void init_sec(configsection *sec, char *name) {
    sec = malloc(sizeof(configsection));
    sec->numopts = 0;
    sec->name = name;
    printf("%s\n", sec->name);
}
// Add a section to a configfile
void add_sec(configfile *cf, configsection *sec) {
    // Increase the size indicator by 1
    cf->numsections = cf->numsections + 1;
    // Reallocate the array to accommodate one more item
    cf->sections = realloc(cf->sections, sizeof(configsection)*cf->numsections);
    // Insert the new item
    cf->sections[cf->numsections] = *sec;
}

I believe my problem originates in my init_sec() function. Here is an example:

int main(void) {

// Initialize test configfile
configfile *cf;
init_file(cf);

// Initialize test configsections
configsection *testcs1;
init_sec(testcs1, "Test Section 1");
// Try printing the value that should have just been stored
printf("test name = %s\n", testcs1->name);

Although the printf() in init_sec() successfully prints the name I just stored in the configsection, attempting the same thing in the printf() of main() produces a segmentation fault. Further, addsec() produces a segmentation fault.

Answer 1

This routine should be

void init_file(configfile **cf) { 
    *cf = malloc(sizeof(configfile)); 
    (*cf)->numsections = 0;
    (*cf)->sections = NULL; // You forgot to initialise this.
}

i.e. called by init_file(&myconfigfilepointer); so the malloc return value gets passed back.

Need to do the same trick for init_sec

This function is incorrect – here is a corrected version

void add_sec(configfile *cf, configsection *sec) {     
    // Increase the size indicator by 1     
    // Reallocate the array to accommodate one more item     
    cf->sections = realloc(cf->sections, sizeof(configsection)*(1 + cf->numsections));     
    // Insert the new item     
    cf->sections[cf->numsections] = *sec; // Since arrays start at 0     
    cf->numsections = cf->numsections + 1;     
} 

You then need to adjust the calls in main