Defined in header <cstdio> | ||
|---|---|---|
int fsetpos( std::FILE* stream, const std::fpos_t* pos ); |
Sets the file position indicator and the multibyte parsing state (if any) for the C file stream stream according to the value pointed to by pos.
Besides establishing new parse state and position, a call to this function undoes the effects of std::ungetc and clears the end-of-file state, if it is set.
If a read or write error occurs, the error indicator (std::ferror) for the stream is set.
| stream | - | file stream to modify |
| pos | - | pointer to a fpos_t object obtained from std::fgetpos called on a stream associated with the same file |
0 upon success, nonzero value otherwise. Also, sets errno on failure.
After seeking to a non-end position in a wide stream, the next call to any output function may render the remainder of the file undefined, e.g. by outputting a multibyte sequence of a different length.
#include <cstdio>
#include <cstdlib>
int main()
{
// Prepare an array of floating-point values.
const int SIZE = 5;
double A[SIZE] = {1., 2., 3., 4., 5.};
// Write array to a file.
std::FILE * fp = std::fopen("test.bin", "wb");
std::fwrite(A, sizeof(double), SIZE, fp);
std::fclose(fp);
// Read the values into array B.
double B[SIZE];
fp = std::fopen("test.bin", "rb");
std::fpos_t pos;
if (std::fgetpos(fp, &pos) != 0) // current position: start of file
{
std::perror("fgetpos()");
std::fprintf(stderr, "fgetpos() failed in file %s at line # %d\n",
__FILE__, __LINE__-3);
std::exit(EXIT_FAILURE);
}
int ret_code = std::fread(B, sizeof(double), 1, fp); // read one value
// current position: after reading one value
std::printf("%.1f; read count = %d\n", B[0], ret_code); // print one value and ret_code
if (std::fsetpos(fp, &pos) != 0) // reset current position to start of file
{
if (std::ferror(fp))
{
std::perror("fsetpos()");
std::fprintf(stderr, "fsetpos() failed in file %s at line # %d\n",
__FILE__, __LINE__-5);
std::exit(EXIT_FAILURE);
}
}
ret_code = std::fread(B, sizeof(double), 1, fp); // re-read first value
std::printf("%.1f; read count = %d\n", B[0], ret_code); // print one value and ret_code
std::fclose(fp);
return EXIT_SUCCESS;
}Output:
1.0; read count = 1 1.0; read count = 1
| gets the file position indicator (function) |
|
| returns the current file position indicator (function) |
|
| moves the file position indicator to a specific location in a file (function) |
|
C documentation for fsetpos |
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