C/C ++: multi-thread programming BASICS (3)

Http://blog.csdn.net/lzx_bupt/article/details/6910632

The thread will be created. How do I pass in parameters when the thread calls a function? It should be as follows:

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2. # Include <iostream>
4. # Include <pthread. h>
8. Using NamespaceSTD;
12. # Define num_threads 5
16. Void* Say_hello (Void* ARGs)
18. {
20. IntI = *((Int*) ARGs );// Forcibly convert the input parameter type, from a non-type pointer to an integer pointer, and then read it;
22. Cout <"Hello in"<I <Endl;
24. }
28. IntMain ()
30. {
32. Pthread_t tids [num_threads];
34. Cout <"Hello in Main ..."<Endl;
36. For(IntI = 0; I <num_threads; ++ I)
38. {
40. IntRet = pthread_create (& tids [I], null, say_hello ,(Void*) & I );// It must be forcibly converted to the void * type when passed in, that is, no type pointer
42. Cout <"Current pthread id ="<Tids [I] <Endl;// Use the tids array to print the ID of the created process;
44. If(Ret! = 0)
46. {
48. Cout <"Pthread_create error: error_code ="<RET <Endl;
50. }
52. }
56. Pthread_exit (null );
58. }

The result is as follows:

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1. Current pthread id = 139671233451792
2. Current pthread id = 139671222961936
3. Current pthread id = 139671212472080
4. Current pthread id = 139671201982224
5. Current pthread id = 139671191492368
6. Hello, in 4196496
7. Hello, in 4196496
8. Hello, in 4196496
9. Hello, in 4196496
10. Hello, in 4196496

Have you found any problems? Yes, the I value does not output the expected results. This is due to multithreading. When the main process has not been assigned a value for I, the thread has started to run !~

Then the followingCodeIs correct:

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2. # Include <iostream>
4. # Include <pthread. h>
8. Using NamespaceSTD;
12. # Define num_threads 5
16. Void* Say_hello (Void* ARGs)
18. {
20. Cout <"Hello in thread"<*((Int*) ARGs) <Endl;
22. }
26. IntMain ()
28. {
30. Pthread_t tids [num_threads];
32. IntIndexes [num_threads];// Use an array to save the I value.
36. For(IntI = 0; I <num_threads; ++ I)
38. {
40. Indexes [I] = I;// Save the I value first, so the problem will not occur in the calling thread.
42. IntRet = pthread_create (& tids [I], null, say_hello ,(Void*) & (Indexes [I]);
44. If(Ret! = 0)
46. {
48. Cout <"Pthread_create error: error_code ="<RET <Endl;
50. }
52. }
54. For(IntI = 0; I <num_threads; ++ I)
56. Pthread_join (tids [I], null );
58. }

Compile and run: (SourceProgramRemove the nonsense of printing thread ID)

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1. [CPP @ node2 pthread] $./ex_create_args_ OK
2. Hello in thread 3
3. Hello in thread 4
4. Hello in thread 2
5. Hello in thread 1
6. Hello in Thread 0