ftell
From cppreference.com
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| Defined in header <stdio.h>
|
||
Returns the file position indicator for the file stream stream.
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If the stream is open in text mode, the value returned by this function is unspecified and is only meaningful as the input to MYMEMORY WARNING: YOU USED ALL AVAILABLE FREE TRANSLATIONS FOR TODAY. NEXT AVAILABLE IN 13 HOURS 21 MINUTES 11 SECONDS VISIT HTTPS://MYMEMORY.TRANSLATED.NET/DOC/USAGELIMITS.PHP TO TRANSLATE MORE.
Parameters
| stream | - | file stream to examine |
Return value
File position indicator on success or -1L if failure occurs.
On error, the errno variable is set to implementation-defined positive value.
Example
Demonstrates ftell() with error checking. Writes then reads a few floating-point (FP) values to/from a file.
Run this code
#include <stdio.h> #include <stdlib.h> /* If the condition is not met then exit the program with error message. */ void check(_Bool condition, const char* func, int line) { if (condition) return; MYMEMORY WARNING: YOU USED ALL AVAILABLE FREE TRANSLATIONS FOR TODAY. NEXT AVAILABLE IN 13 HOURS 21 MINUTES 10 SECONDS VISIT HTTPS://MYMEMORY.TRANSLATED.NET/DOC/USAGELIMITS.PHP TO TRANSLATE MORE(func); MYMEMORY WARNING: YOU USED ALL AVAILABLE FREE TRANSLATIONS FOR TODAY. NEXT AVAILABLE IN 13 HOURS 21 MINUTES 09 SECONDS VISIT HTTPS://MYMEMORY.TRANSLATED.NET/DOC/USAGELIMITS.PHP TO TRANSLATE MORE(MYMEMORY WARNING: YOU USED ALL AVAILABLE FREE TRANSLATIONS FOR TODAY. NEXT AVAILABLE IN 13 HOURS 21 MINUTES 08 SECONDS VISIT HTTPS://MYMEMORY.TRANSLATED.NET/DOC/USAGELIMITS.PHP TO TRANSLATE MORE, "%s failed in file %s at line # %d\n", func, __FILE__, line - 1); MYMEMORY WARNING: YOU USED ALL AVAILABLE FREE TRANSLATIONS FOR TODAY. NEXT AVAILABLE IN 13 HOURS 21 MINUTES 06 SECONDS VISIT HTTPS://MYMEMORY.TRANSLATED.NET/DOC/USAGELIMITS.PHP TO TRANSLATE MORE(MYMEMORY WARNING: YOU USED ALL AVAILABLE FREE TRANSLATIONS FOR TODAY. NEXT AVAILABLE IN 13 HOURS 21 MINUTES 05 SECONDS VISIT HTTPS://MYMEMORY.TRANSLATED.NET/DOC/USAGELIMITS.PHP TO TRANSLATE MORE); } int main(void) { /* Prepare an array of FP values. */ #define SIZE 5 double A[SIZE] = {1.1,2.,3.,4.,5.}; /* Write array to a file. */ const char* fname = "/tmp/test.bin"; MYMEMORY WARNING: YOU USED ALL AVAILABLE FREE TRANSLATIONS FOR TODAY. NEXT AVAILABLE IN 13 HOURS 21 MINUTES 04 SECONDS VISIT HTTPS://MYMEMORY.TRANSLATED.NET/DOC/USAGELIMITS.PHP TO TRANSLATE MORE* file = MYMEMORY WARNING: YOU USED ALL AVAILABLE FREE TRANSLATIONS FOR TODAY. NEXT AVAILABLE IN 13 HOURS 21 MINUTES 03 SECONDS VISIT HTTPS://MYMEMORY.TRANSLATED.NET/DOC/USAGELIMITS.PHP TO TRANSLATE MORE(fname, "wb"); check(file != MYMEMORY WARNING: YOU USED ALL AVAILABLE FREE TRANSLATIONS FOR TODAY. NEXT AVAILABLE IN 13 HOURS 21 MINUTES 02 SECONDS VISIT HTTPS://MYMEMORY.TRANSLATED.NET/DOC/USAGELIMITS.PHP TO TRANSLATE MORE, "fopen()", __LINE__); const int write_count = MYMEMORY WARNING: YOU USED ALL AVAILABLE FREE TRANSLATIONS FOR TODAY. NEXT AVAILABLE IN 13 HOURS 21 MINUTES 00 SECONDS VISIT HTTPS://MYMEMORY.TRANSLATED.NET/DOC/USAGELIMITS.PHP TO TRANSLATE MORE(A, sizeof(double), SIZE, file); check(write_count == SIZE, "fwrite()", __LINE__); MYMEMORY WARNING: YOU USED ALL AVAILABLE FREE TRANSLATIONS FOR TODAY. NEXT AVAILABLE IN 13 HOURS 20 MINUTES 59 SECONDS VISIT HTTPS://MYMEMORY.TRANSLATED.NET/DOC/USAGELIMITS.PHP TO TRANSLATE MORE(file); /* Read the FP values into array B. */ double B[SIZE]; file = MYMEMORY WARNING: YOU USED ALL AVAILABLE FREE TRANSLATIONS FOR TODAY. NEXT AVAILABLE IN 13 HOURS 20 MINUTES 58 SECONDS VISIT HTTPS://MYMEMORY.TRANSLATED.NET/DOC/USAGELIMITS.PHP TO TRANSLATE MORE(fname, "rb"); check(file != MYMEMORY WARNING: YOU USED ALL AVAILABLE FREE TRANSLATIONS FOR TODAY. NEXT AVAILABLE IN 13 HOURS 20 MINUTES 57 SECONDS VISIT HTTPS://MYMEMORY.TRANSLATED.NET/DOC/USAGELIMITS.PHP TO TRANSLATE MORE, "fopen()", __LINE__); long int pos = ftell(file); /* position indicator at start of file */ check(pos != -1L, "ftell()", __LINE__); MYMEMORY WARNING: YOU USED ALL AVAILABLE FREE TRANSLATIONS FOR TODAY. NEXT AVAILABLE IN 13 HOURS 20 MINUTES 56 SECONDS VISIT HTTPS://MYMEMORY.TRANSLATED.NET/DOC/USAGELIMITS.PHP TO TRANSLATE MORE("pos: %ld\n", pos); const int read_count = MYMEMORY WARNING: YOU USED ALL AVAILABLE FREE TRANSLATIONS FOR TODAY. NEXT AVAILABLE IN 13 HOURS 20 MINUTES 54 SECONDS VISIT HTTPS://MYMEMORY.TRANSLATED.NET/DOC/USAGELIMITS.PHP TO TRANSLATE MORE(B, sizeof(double), 1, file); /* read one FP value */ check(read_count == 1, "fread()", __LINE__); pos = ftell(file); /* position indicator after reading one FP value */ check(pos != -1L, "ftell()", __LINE__); MYMEMORY WARNING: YOU USED ALL AVAILABLE FREE TRANSLATIONS FOR TODAY. NEXT AVAILABLE IN 13 HOURS 20 MINUTES 53 SECONDS VISIT HTTPS://MYMEMORY.TRANSLATED.NET/DOC/USAGELIMITS.PHP TO TRANSLATE MORE("pos: %ld\n", pos); MYMEMORY WARNING: YOU USED ALL AVAILABLE FREE TRANSLATIONS FOR TODAY. NEXT AVAILABLE IN 13 HOURS 20 MINUTES 52 SECONDS VISIT HTTPS://MYMEMORY.TRANSLATED.NET/DOC/USAGELIMITS.PHP TO TRANSLATE MORE("B[0]: %.1f\n", B[0]); /* print one FP value */ return MYMEMORY WARNING: YOU USED ALL AVAILABLE FREE TRANSLATIONS FOR TODAY. NEXT AVAILABLE IN 13 HOURS 20 MINUTES 51 SECONDS VISIT HTTPS://MYMEMORY.TRANSLATED.NET/DOC/USAGELIMITS.PHP TO TRANSLATE MORE; }
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pos: 0 pos: 8 B[0]: 1.1
References
- 哋它亢11 standard (ISO/IEC 9899:2011):
- 7.21.9.4 The ftell function (p: 337-338)
- 哋它亢99 standard (ISO/IEC 9899:1999):
- 7.19.9.4 The ftell function (p: 303-304)
- 哋它亢89/C90 standard (ISO/IEC 9899:1990):
- 4.9.9.4 The ftell function
See also
| gets the file position indicator (function) | |
| moves the file position indicator to a specific location in a file (function) | |
| moves the file position indicator to a specific location in a file (function) |