strchr(), strchr

Find the first occurrence of a character in a string

Synopsis:

#include <string.h>

char* strchr( char* s, 
              int c );

char* strchr_isr( char* s, 
                  int c );

Arguments:

s: The string that you want to search.
c: The character that you're looking for.

Library:

libc

Use the -l c option to qcc to link against this library. This library is usually included automatically.

Description:

The strchr() function finds the first occurrence of c (converted to a char) in the string pointed to by s. The terminating NUL character is considered to be part of the string. The strchr_isr() is similar, but it's safe for you to use it in an interrupt service routine.

Returns:

A pointer to the located character, or NULL if c doesn't occur in the string.

Examples:

#include <stdio.h>
#include <string.h>
#include <stdlib.h>

int main( void )
{
    char buffer[80];
    char* where;

    strcpy( buffer, "video x-rays" );

    where = strchr( buffer, 'x' );

    if( where == NULL ) {
        printf( "'x' not found\n" );
    } else {
        printf( "'x' found: %s\n", where );
    }

    return EXIT_SUCCESS;
}

Environment variables:

LIBC_STRINGS

On certain targets, you can use this environment variable to select the implementation of strchr(). It doesn't affect the implementation of strchr_isr(). The value is one of the strings given below.

for AArch64 targets:
- aarch64_neon — optimized for AARCH64 targets using NEON
- generic — the default
for ARMv7 targets:
- cortex_a9 — optimized for the ARM Cortex-A9 processor; assumes that no unaligned access is supported
- cortex_a9_aligned — optimized for ARM Cortex-A9; requires that unaligned memory access be enabled on the platform. If memory access is misaligned, this implementation falls back to the NEON version.
- cortex_a9_neon — optimized for ARM Cortex-A9 using NEON
- generic — the default
- krait — optimized for the Qualcomm Krait CPU
- krait_neon — optimized for Qualcomm Krait using NEON

Processes that register ISRs shouldn't use the NEON versions.

Classification:

strchr() is ANSI, POSIX 1003.1; strchr_isr() is QNX Neutrino.

Table 1. strchr()
Safety:
Cancellation point	No
Interrupt handler	Read the Caveats
Signal handler	Yes
Thread	Yes

Table 2. strchr_isr()
Safety:
Cancellation point	No
Interrupt handler	Yes
Signal handler	Yes
Thread	Yes

Caveats:

Implementations of strchr() that are optimized using SIMD instructions aren't safe to use in an interrupt handler. These include the NEON implementations on ARMv7 and AArch64.

strchr(), strchr_isr()