Hi, need to dynamicaly create/resize a char array which is a field in a struct. The struct is an element in an array of structs. the code compiles ok but the program crashes whenever I run it, i.e. doesn't end or exit. The code: #include #include #include #include extern int errno; struct stuff { char *dave, *temp_dave; int steve; }; int main() { struct stuff *mate=NULL, *temp_mate; mate=(struct stuff *)malloc(sizeof(struct stuff)); if(mate=NULL) { perror("malloc\n"); exit(1); } mate[0].dave=(char *)malloc(sizeof(char)); if(mate[0].dave==NULL) { perror("malloc\n"); exit(1); } temp_mate=(struct stuff *)realloc(mate, sizeof(struct stuff)+sizeof(struct stuff)); if(temp_mate==NULL) { perror("realloc\n"); exit(1); } mate=temp_mate; free(mate[0].dave); free(temp_mate); printf("\nexit ok\n"); return 0; } any ideas, or suggestions? Cos I'm all out. Any help would be greatly appreciated.

Try making mate, mate[0], and temp_mate NULL terminated. That's fixed my problems before.

thanks for your response.  Had a bit of a long day.  could you explain a little more? did you mean changing this line struct stuff *mate=NULL, *temp_mate; to this? struct stuff mate[0]=NULL, *temp_mate=NULL;? I've tried it and it generates loads of errors.

Alright, 2 problems: if(mate=NULL) { Should be: if(mate==NULL) { And: mate[0].dave=(char *)malloc(sizeof(char)); if(mate[0].dave==NULL) { mate[0].dave wont = NULL, it needs to be set first: mate[0].dave=NULL; mate[0].dave=(char *)malloc(sizeof(char)); if(mate[0].dave==NULL) { hope that helps... -Micah

brilliant, thanks. I've had some sleep now and it all makes sense.

It looks like this code is just a test to see that you can realloc and doesn't really do anything. But, for the future, I see two 'issues': mate[0].dave=(char *)malloc(sizeof(char)); You are allocating only one byte here for the array 'dave'. Obviously, not enough room to put a string in there. But, maybe that was just for this test. More importantly, in the code: temp_mate=(struct stuff *)realloc(mate, sizeof(struct stuff)+sizeof(struct stuff)); Note that for the structure 'mate', you did two mallocs, one to allocate the structure 'mate' and one to allocate some memory for the 'dave' array. But in creating temp_mate, you use only one allocation call (realloc). So you've made a new copy of 'mate' in 'temp_mate'. But this realloc() does not allocate memory for the 'dave' array in 'temp_mate'. I'm 99% sure that realloc() copies the contents from 'mate' to 'temp_mate', so temp_mate->dave will contain a pointer to the same memory as mate->dave. If this is what you want, that's fine. But if you want temp_mate->dave to be a separate array from mate->dave, then you need to run another malloc for temp_mate->dave. Finally: mate=temp_mate; Since you didn't free 'mate' before copying 'temp_mate' to it, you now have a bit of memory (the allocation of the original 'mate' structure) hanging out with no pointer, so you can't free it.

I just noticed the syntax that you used. In case it throws you, mate->dave is the basically the same as mate[0].dave Personall, I wouldn't use mate[0] in this situation because that implies that mate is an array. I guess technically you could say that it is an array, an array of one element, but...