Using errno for Error Reporting
When you work with C programs that interact with the system or perform input/output operations, you may encounter situations where a function fails. The C standard library uses a global variable called errno to provide more information about such errors. The errno variable is set by library functions when an error occurs, allowing you to determine the specific cause of the failure. For instance, if you try to open a file that does not exist using fopen, the function returns NULL and sets errno to a value that indicates the reason for the error. You can then use the strerror function to convert the errno value into a human-readable error message, which is very useful for debugging and reporting errors to users.
main.c
123456789101112#include <stdio.h> #include <errno.h> #include <string.h> int main() { FILE *file = fopen("nonexistent.txt", "r"); if (file == NULL) printf("Error opening file: %s\n", strerror(errno)); else fclose(file); return 0; }
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When you work with C programs that interact with the system or perform input/output operations, you may encounter situations where a function fails. The C standard library uses a global variable called errno to provide more information about such errors. The errno variable is set by library functions when an error occurs, allowing you to determine the specific cause of the failure. For instance, if you try to open a file that does not exist using fopen, the function returns NULL and sets errno to a value that indicates the reason for the error. You can then use the strerror function to convert the errno value into a human-readable error message, which is very useful for debugging and reporting errors to users.
main.c
123456789101112#include <stdio.h> #include <errno.h> #include <string.h> int main() { FILE *file = fopen("nonexistent.txt", "r"); if (file == NULL) printf("Error opening file: %s\n", strerror(errno)); else fclose(file); return 0; }
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