To open a file in Append mode, set offset is invalid

1#include <stdio.h>2 3 intMain ()4 {5FILE * fd = fopen ("btoo1.c","ab+");6 fpos_t p;7     intfp = Fgetpos (FD, &p);8printf"bef Seek:fgetpos =%ld, Ftell =%d\n", p, Ftell (FD));9Fseek (FD, A, seek_set);TenFgetpos (FD, &p); Oneprintf"bef Seek:fgetpos =%ld, Ftell =%d\n", p, Ftell (FD)); AFwrite"*****",1,5, FD); - fclose (FD); -     return 0; the}

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Test the code as above. The phenomenon is so, the reason is unknown.

Solution:

Set the temporary file, write the content before the offset to the 0 o'clock file, delete the source file, and then rename the zero file.