What is vfscanf_s in C?
The vfscanf_s function
The function vfscanf_s is defined in the stdio.h standard library and is used to read data from a file stream. The structure
of the vfscanf_s function is as follows:
int vfscanf_s(FILE * stream, const char * format, va_list arglist);
Parameters
streamis a pointer to aFILEstructure.formatis a pointer to a character array which represents a format string.arglistis a list of arguments required by theformatstring.
Return value
- A positive number specifying the number of fields successfully read and assigned.
EOFif an error occurs or the end of the stream is reached.
Example usage of the vfscanf_s function
The following code demonstrates the use of the vfscanf_s function:
#include<stdio.h>/*call_vfscanf_s is a wrapper function which converts "..." to "arglist" and calls vfscanf_s function*/int call_vfscanf_s(FILE * stream, char * format, ...) {int result;va_list arglist;va_start(arglist, format);result = vfscanf_s(stream, format, arglist);va_end(arglist);return result;}int main() {char text[10];int score_obtained;int total_score;/*Contents of file "temp.txt":Score: 8 10*/FILE * stream = fopen("temp.txt", "r");call_vfscanf_s(stream, "%s %d %d", &text, &score_obtained, &total_score);fclose(stream);printf("Score Obtained: %d\n", score_obtained);printf("Total Score: %d\n", total_score);return 0;}
Output:
Score Obtained: 8
Total Score: 10
In the example above, a file temp.txt is read using the function vfscanf_s by opening a file stream in line 23. The result of the file is stored in 3 variables: text, score_obtained, and total_score, as specified by the format string %s %d %d and the order of the said 3 variables passed to the call_vfscanf_s function. The variables text, score_obtained, and total_score stored Score:, 8, and 10 respectively. Finally, the score_obtained and the total_score were printed onto the standard output.
Note: The function above is not supported by the GCC compiler, so you will get an
implicit declaration of function…error.
Use the following function vfscanf to get the job done:
int vfscanf(FILE * stream, const char * format, va_list arglist);
All parameters and return values are the same as the vfscanf_s function.
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