c initialize an array of structs of structs

Question

I have 2 structs, path and paths. Then, define an array of paths to hold my data:

enum MAX_NEIGHBOR {MAX_NEIGHBOR = 256}; enum MAX_NUM_PATHS {MAX_NUM_PATHS = 100}; typedef struct { int id; int path[MAX_NEIGHBOR]; } path; typedef struct { int id; path pathsIKnow[MAX_NUM_PATHS]; } paths; paths pathsIKnow[MAX_NEIGHBOR];

I am currently initializing the array in a big loop at runtime, which takes too much time. Is there a way I can initialize this without a loop, such as during definition of the paths array?

Current loop code:

void initKnownPaths() { for(int j=0;j<MAX_NEIGHBOR;j++){ paths pathsToI = pathsIKnow[j]; pathsToI.id = 999; for(int i=0 ;i < MAX_NUM_PATHS;i ++){ path pathToupdate = pathsToI.pathsIKnow[i]; pathToupdate.id = 999; for(int j=0 ;j < MAX_NEIGHBOR;j++){ int cPathValue = pathToupdate.path[j]; cPathValue = 999; pathToupdate.path[j] = cPathValue; } pathsToI.pathsIKnow[i] = pathToupdate; pathsIKnow[j] = pathsToI; } } }

Thanks!

Your init function is copying large amounts of data around, and is doing a lot of work that gets thrown away. You should clean that up first. Also, having two different variables named j is just asking for trouble. — 1201ProgramAlarm
– 1201ProgramAlarm, Commented Oct 28, 2019 at 0:57

Saurabh P Bhandari · Accepted Answer · 2019-12-15 09:08:59Z

If you are compiling using GCC, then instead of initKnownPaths function you can replace the structure variable pathsIKnow of type struct paths by this:

paths pathsIKnow[MAX_NEIGHBOR] = { [0 ... MAX_NEIGHBOR - 1] = { 999, { [0 ... MAX_NUM_PATHS - 1] = { 999, { [0 ... MAX_NEIGHBOR - 1] = 999}}}}};

If you are not using GCC, then you should improve your existing function based on @1201ProgramAlarm's suggestions

Note: If you use the first method, your compiled binary file size will increase, however this should reduce the run-time. (time-space tradeoff !!)

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